Even though a battery maintainer is a “set it and forget it” type of thing, it’s still recommended to check on your batteries at least quarterly throughout the year.
If you have a sealed battery, there’s not much you’re going to be able to do as these batteries are mostly maintenance-free. Any water lost due to the charging process is recycled back into the solution as long as the overcharging was not excessive.
Just look for any corrosion and carry on as normal as long as the voltage reading still looks like it’s in the appropriate range on the electronic voltmeter.
If you have a flooded battery, remove the caps and check the water levels. On my batteries, I normally have to add about 10 ml of water per cell every 3 months or so. Use only distilled water, and I recommend using a plastic syringe for children’s medication to carefully inject the water instead of attempting to pour it from a jug.
After you lift the cap off a flooded lead-acid battery you’ll see this. The red line is the edge of the slotted fill tube. The blue is the water curve beneath it. The green is the 1/8″ space between. You can see the lead plates at the bottom of the hole, and the slot for the fill tube at the top of the hole.
It’s also a good idea to use a hydrometer to check the specific gravity in each of the cells. This is how you will be able to determine if you’ve got a cell that’s going bad in your battery. It only takes one weak or bad cell to ruin the rest of your battery through overcharging.
The overcharging happens when the charger/maintainer will read the total voltage of your battery (which should be around 12.6-12.7 when fully charged for a 12-volt battery). Each cell (there are 6 in a 12-volt battery) should measure at 2.1 volts when fully charged.
If a cell has gone bad or is compromised, the charger might read the entire battery at 10.5, for example, and do its best to bring the total charge up to 12.6-12.7 — but it would be raising the 5 functioning cells to that level and not the 6th one which is now bad (likely due to sulfation).
In order to get to 12.6-12.7, each cell would have to be 2.52+ volts… and they simply cannot support this. The water will quickly evaporate from the electrolyte and leave you with exposed lead plates which will start to sulfate as well.
Are solar batteries safe?
Yes! In general, solar batteries are very safe. Issues that may arise come if they are installed incorrectly or the battery quality is low. Because of that, it is important to ensure batteries are properly installed, in suitable condition, and purchased from a reputable manufacturer.
For example, Renogy deep cycle solar batteries have a BMS, which stands for Battery Management System. The BMS safely protects the battery from being used/charged during incorrect conditions.