When you’re purchasing your first battery charger, it is easy to get overwhelmed by the sheer number of options that you’ll find online or at your local big box store — whether it be a Battery Tender®, a battery charger, a battery maintainer, a trickle charger, a 3-stage smart charger, etc.
If your aim is to simply hook up a charger to a car, boat, or golf cart battery and have it be ready to go in the morning, then you’ll likely find yourself between these two options: a Battery Tender®, or a trickle charger.
Are they even different, or different enough to worry about, or are we just splitting hairs?
The term Battery Tender® is a trademarked name, whereas the terms “trickle charger” and “battery maintainer” are describing features of any brand of charging devices — including a Battery Tender®.
To put it plainly, a Battery Tender® device can trickle (slow) charge your battery, but it can also maintain your battery at 100% state of charge so that your battery is not damaged from overcharging. A Battery Tender® is a trademarked name but is also a trickle charger and a maintainer as far as how it functions.
On the other hand, a generic “trickle charger” might have the same tricks up its sleeve, or it might be a one trick pony. It might be safe to leave hooked-up to your battery indefinitely, or it might cook your battery to death. In other words, it may be a “trickle charger”, but it may not be a “maintainer”.
Let’s jump into what you can expect from a Battery Tender®, what a “trickle charger” is, what a “maintainer” is, and what you want to look for when purchasing a charging device to meet your needs!
What is a Battery Tender®?
As we mentioned above, a Battery Tender® is a trademarked name covering a variety of models, and both “trickle charging” and “battery maintaining” are included features.
As a feature, a Battery Tender® can certainly trickle charge your battery. But what happens when the battery is fully charged?
That’s where a Battery Tender® is an ideal choice for anyone who wants a user-friendly charging device that can simply be hooked-up and forgotten about until they are ready to use that battery again. Simply put, it maintains the battery after charging without needing to be disconnected.
A Battery Tender® incorporates a 4-stage, microprocessor-controlled process when moving through the entire charging process and they are as follows:
- Initialization: The safety check to verify voltage, polarity, and secure connections
- Bulk Mode: Full current and voltage to bring the battery from 0% to 80% state of charge
- Absorption Mode: High voltage, reduced current to bring the battery from 80% to 100% state of charge
- Float Mode: Low constant voltage that matches the battery’s self-discharge rate to safely keep it topped off
Essentially, a Battery Tender® can precisely detect exactly what voltage and amperage your battery needs at every step of the charging process in order to safely charge it and maintain it without cooking off the electrolyte due to overcharging.
Remember, your car or boat battery is trying to convert electrical energy from your charging device into stored chemical energy. It can only do so at a certain rate and that rate depends on the state of charge of the battery at any given moment. The same voltage and amperage used to bring up a battery from 0-80% would easily cook off the electrolyte if it were used to bring it up from 80-100% and beyond.
Teaching Tool: Think of charging a battery like blowing up a balloon to 100% capacity without popping it. When the balloon is empty, you can blow lots of air (amperage) with lots of pressure (voltage).
As the balloon reaches 80%, you intuitively reduce the amount of air (amperage) and actually keep the pressure high (voltage) since the balloon also wants to push the air back out at you (internal resistance).
If you couldn’t tie it off, you would effectively need to only provide air (amperage) if a negligible amount escaped (self-discharge) and you would need to reduce the pressure (voltage) to exactly match the pressure of the balloon’s so that air could neither enter nor escape.
With the image of that balloon in your head, imagine if you simply kept blowing up the balloon at the same rate from start to finish. You would quickly pop your balloon after you maxed out its capacity. Even if you slowed down, but didn’t know when to turn off the amperage, you would still pop it.
A Battery Tender® is microprocessor-controlled to precisely monitor and maintain what the battery needs by the millisecond.
To put it plainly, a Battery Tender® will gently and perfectly blow up that balloon in our example to 100% capacity every time, and it will keep it there without popping the balloon.
| Battery Tender® Pros | Battery Tender® Cons |
|---|---|
| Affordably priced | Offered models may be too small (amperage) for larger systems (100AH+) if you expect a fast charge (depending on the model) |
| Generally a slower, gentler charge | Lacks an optional (or even automatic) desulfation/equalization mode (or is not advertised) |
| Nearly all models maintain battery health after charging and can be left connected indefinitely | If battery (12v) is dead and lower than 9-volts, the charger will not recognize it and will not charge (see “Pro Tip” below) |
| Very user-friendly with built-in safety features | |
| Many amperage ratings to choose from (0.75amps-15amps) |
Pro Tip: If your 12-volt battery is below 9-volts due to leaving the lights on your lawn tractor for a week, for example, you will find that many smart chargers will not recognize it and will not charge. Hooking your dead battery up to a working car battery with jumper cables, running the vehicle for 5 minutes, disconnecting the jumper cables and reconnecting the charger will usually give it the surface charge needed to start the charging process!
What is a Trickle Charger?
As was mentioned before, a “trickle charger” is a descriptive term for a feature that a charger possesses.
As a general rule, a “trickle charger” is a term for any battery charger with low amperage that slowly charges a battery, often taking a full 24 hours or more. A trickle charger may actually harm a battery if left connected for extended periods of time if it isn’t designed to maintain a battery after it is fully charged.
Generally, you’ll commonly find that chargers between 0.75 amps and 4 amps are referred to as “trickle chargers”.
It’s relative, though, and you need to consider the size of the battery when referring to a charger as a “trickle charger”.
If you have a 4 amp charger on a 100AH (amp hour) battery, then it could very well be considered by some to be a “trickle charger”. If the same charger was hooked up to a 12AH battery, then the charger would now have an amp rating that was 1/3 the total capacity of the battery itself! That would definitely be considered worthy of dropping the “trickle” prefix and simply be labeled a “charger”, for all intents and purposes.
If the amp rating of the charger is 5% or less of the total amp hour rating of the battery that is being charged, it probably wouldn’t raise any eyebrows if you referred to it as a “trickle charger”.
Trickle chargers may or may not maintain the battery once it reaches 100% state of charge. You will want to check the owners manual of your particular trickle charger to see what it says about any “maintenance” or “float” modes.
If you need to see how long you can expect it to take for any given charger to charge your battery, you can check out my article here which has some easy to use calculators where you simply plug in your values and are given a time. There is a quick video tutorial as well within the article to guide you through the process.
If the charger says to disconnect the leads after it reaches 100%, then it is best to do so. If you leave it hooked up too long, even a small trickle of a current can boil off the electrolyte within the battery, resulting is reduced performance and battery failure if left connected for too long.
Remember that a battery converts electrical energy into stored chemical energy. If the battery is already at 100% and the trickle charger doesn’t enter into float mode and instead keeps giving the battery a small current, then there is nothing left to convert. The battery has already reached its full conversion potential.
The excess electricity creates heat within the battery and that heat is released when the electrolyte inside the battery boils off and evaporates away.
In a flooded lead acid battery (the kind where to pop the caps to check the levels inside), distilled water can be added back to mitigate this to a degree.
In a sealed battery (Gel, AGM), this electrolyte can be recombined within the battery itself unless the pressure builds up too high (depends on the amps of your charger) and then it can leak out through a pressure relief valve. If electrolyte is lost in a sealed battery, it cannot be replaced and the battery is permanently damaged. The extent to which it is damaged depends on how long it was allowed to overcharge.
Again, feel free to click here to see how long it takes to charge your battery with a given charger so that you don’t risk overcharging it if the charger doesn’t automatically stop.
What is a Battery Maintainer?
A battery maintainer, or float charger, is any brand of charging device that will cease charging when a battery reaches 100% state of charge, and will only emit a small current when the battery naturally self-discharges over time. These can be left connected for a full season or more without damaging the battery.
Every model of Battery Tender® charging devices that I’m aware of will also maintain your batteries after they are fully charged, and this is my favorite model from Amazon to maintain your car’s battery over the winter.
To know if your charger is also a maintainer, it should be labeled somewhere on the device itself. You should see the words “maintainer” or “float mode” somewhere on it. If you don’t see anything, consult the manual.
If your charger or manual say to disconnect the battery after it has reached 100% state of charge, then you likely do not have a battery maintainer.
What are the Best Trickle Chargers?
Before selecting any charger, you want to take note of the following things:
- Your battery’s total amp hours in relation to the amp rating of the charger (10% rule, explained below)
- How many volts your battery is (6, 8, 12, 24, etc.)
- What type of battery you have (flooded, gel, AGM, Li(LiFePO4), etc.)
Regardless of what battery charger you select, it is a good rule of thumb to never have the amps of the charger exceed 10% of the total amp hours of the battery in question.
The more you exceed 10%, the higher the risk of your battery overcharging since it won’t be able to convert electrical energy into stored chemical energy fast enough to keep up with the charger’s output. The result will be overcharging and reducing your battery’s life and function.
So, a 100AH battery shouldn’t generally have a charger above 10amps.
Since we’re talking about “trickle chargers” in this article, my recommendations are going to be on the lower end of the amp ratings.
Is there anything wrong with using a 2-amp charger instead of a 10-amp charger on a 100AH battery? Nope, and vice versa.
The 2-amp charger will just take a lot longer (2.5 days vs. 11 hours on a dead battery) — but the reduced amperage will allow the battery to get a better charge and perform a bit better since it can convert the electrical energy into stored chemical energy more efficiently and effectively.
Next, consider how many volts your battery is. If you buy a 12-volt, 2-amp “trickle charger” and you hook it up to a 6-volt golf cart battery, it’s either not going to work, or you’re not going to like the result. Make sure the volts of your battery (check its label) match the volts of the charger.
Finally, make sure the charger you select has the capability to charge your particular battery type. Not all chargers that work great for flooded lead acid batteries are suitable for AGM batteries, or Li(LiFePO4). In fact, you can damage or destroy the batteries by doing so. Some chargers are good for one type, some will cover a spectrum.
The Deltran Battery Tender® line of chargers is great at accommodating all battery types in many (but not all) of its models, and the same can be said for NOCO brand battery chargers as well. Both brands also offer many models that have options to switch between 6-volts and 12-volts, or 12-volts and 24-volts.
I have a table below of 12-volt “trickle chargers” that I have used or would use, and recommend. These can ALL be left connected to your battery indefinitely!
| Battery Application | Recommended “Trickle Charger” Amp Range | Recommended “Trickle Chargers” (Amazon) |
|---|---|---|
| Car | 2-4 Amps | 2-Amp Noco Genius® 4-Amp Battery Tender® |
| Boat (Marine) | 2-5 Amps | 4-Amp Battery Tender® 5-Amp Noco Genius® |
| Lawn Tractor, Motorcycle, ATV | 750mA – 1.25 Amps | 750mA Battery Tender® 1.25-Amp Battery Tender® (12 or 6 volts) |
| Golf Cart (6-Volt) | 2-4 Amps | 2-Bank, 4-Amp (2 per bank) 6 or 12 Volt Noco Genius® You can hook up 2 x 6 volt batteries on each bank, or use the 12-volt setting if you have 2 x 6-volt batteries hooked in series 4-Amp Battery Tender® |