Originally Posted by TN_GLC300

More good information ^^^^^^^ except for leaving a battery on a 'Maintainer' for any length of time. Yes, a Maintainer will sense when the voltage drops to a level where the charger will kick in again and top off the battery. The problem with this is with a wet cell LA battery, the electrolyte starts boiling again trying to maintain a constant state of full charge. Every time this happens, your battery is losing more electrolyte killing your battery. With our AGM batteries, I'm not quite sure what the behavior is because AGM batteries are constructed differently. Although I suspect the behavior is the same just in another form. Also, if your 'Maintainer' is not specifically designed for AGM batteries, the AGM battery will never reach a full charge as the charging voltages are different than regular LA batteries. No battery likes to be in a constant state of full charge. Just like your cell phone. The recommended state of charge for your cell phone is between 40-80% and to never leave it plugged into the charger. Yes, I know cell phone batteries are a different chemistry but the common theme here is a constant state of full charge for any battery chemistry is detrimental to the longevity of the battery. Everyone's mileage will vary but I've killed more batteries trying to leave them in a constant state of full charge than just topping them off occasionally. Maintainers have there uses but should never be left on for any length of time. Especially if they are left unattended.

If you want to significantly extend the life of your Wet cell/AGM LA Battery, do the following:

1. Never run any battery below 25% capacity. Doing so will permanently harm your battery.

2. At least once a month, depending on car model, connect a smart battery charger specific for the chemistry battery you are trying to charge. In other words, you need an AGM specific smart battery charger. I recommend the CTEK or NOCO smart chargers. They have an AGM specific switch on them. Batteries like to be charged with low current. I use the CTEK 5.0 as my primary charger. Yes, it takes longer but I've found >10A chargers can and often overcharge and confuse battery termination algorithms. Low current smart chargers take longer but are much safer and offer a more thorough charge in my experience. They also are less likely to boil off your electrolyte like higher current smart chargers will. The temperature of your environment needs to be between 60F-80F. I know for a lot of folks this will be a problem but batteries do not like extremes on either end of the scale.

I live in a rural area and my GLC is stored in a covered garage so the car is constantly trying to find signal and stay connected to the cloud draining my battery. My original battery will pretty much be in a deep state of discharge in 4-5 days if I don't drive it or recharge it. My GLC is not my principle driver so it's easier for me to just top it off every 4-5 days with my charger. I never leave the charger connected for more than 24-hrs after it finishes charging. My original battery is just over 5 years old and showing no signs of degradation. For those who use there GLC's daily or more often, just top your battery off once a month with a smart charger and you should get 5-7 years from your battery easily no matter who makes it. I also recommend you let your car sit undriven for 12-hrs for your battery to reach a resting/steady state before charging. Trying to charge the battery right after driving it will usually give a smart charger a false sense of battery charge.