A motorcycle battery tender is an equipment to maintain two wheelers. They come in pre-packaged kits and they are a type of trickle battery charger- it never overcharges and charges really slowly. It incorporates “constant current, constant voltage, multi step charging.” Even if you store the battery for days, it does not lose its charge and is always ready for discharge.
Car batteries have lead plates inside and filled with sulfuric acid which creates a chemical reaction which in turn creates the electricity. The battery also produces lead sulfate during this process which will eventually leave lead sulfate deposits on the lead plates.
This over-charges the battery and reduces the the life span of the battery. This is particularly noticeable for those that like to always keep their battery on a charger when not in use.
Gassing: When the cell is fully charged, it starts liberating the gas freely. In restoring a battery the hydrogen is liberated at cathode while oxygen at the anode. Gassing is a good indication of fully charged battery. Some acid particles may go out with the gases hence the charging room must be kept well ventilated.
The next best is the gel type reconditioning battery. These won’t leak, but as you might expect, they are more expensive than the wet lead-acid type battery.
Inspecting your battery from time to time is a good idea, as corrosion never sleeps, and can ruin your battery cables if left for too long. Modern battery cables are complicated affairs, and they are not cheap! Also, manufacturers like to hide batteries under covers and even in the trunk sometimes, as if they really were maintenance free.
Since lithium batteries are everywhere in small electronics, the personal solar chargers are designed around them. This is why the USB format has become the standard for charging small electronics – the 3.7V lithium cell charges from the 5V USB. Lithium batteries in small electronics also comes with their own built-in controller that stops them from being charged once they are full.