Originally Posted by Pied Typer
Remember, it is a generally accepted rule that you have to drain your battery to a certain point (read not entirely but not too little) before you should recharge them. They only have so many recharge cycles in them (though it is not a fixed number) and you want to maximize this number.
This is true of nickel-cadmium rechargeable batteries used in electronic devices, which develop a "memory" if not discharged to 1 volt per cell. Nickel-metal-hydride batteries have pretty much replaced NiCads because of this. Lithium-ion carry more power for weight and size, but need "smart" charging, and only have about 1/3 the recharges of a NiMH pack.
Wet cells last for more recharges if they are discharged less and refilled more often. I saw a manufacturer's chart once but don't remember where, which had a graph curve that showed the number of recharges versus the depth of each discharge. They rated their batteries for only three
100% discharges! This is why a lot of people try not to draw a battery below 50%, or about 12 volts.
I see one of three problems in the original post:
1. The trickle charger does not stop when the batteries are full, boils off some acid, exposing the tops of the plates and poisoning them. I would recommend a constantly connected "float" charger put out no more than 13.5 volts into a full battery. And still check the acid level. Or, disconnect the battery when the bus is stored with either a switch or wire removal. A fully-charged good battery with a clean top should not self-discharge (much) when disconnected.
2. There is a poor connection somewhere, so some of the charging power is being burned up as heat before it reaches the batteries, and they are not getting filled. Clean the connections.
3. The "trickle" charger is too small to power loads, fill the batteries, and overcome losses. A bigger charger would be needed (but see #1).
A battery is a storage tank that keeps electricity stored as a chemical reaction. You have to put fuel into the 'tank' in order to draw it back out. Electricity seems mysterious, but really isn't. Think in terms of storing other energy. Imagine if someone wrote:
I have a 100 gallon fuel tank, and get 10 miles to the gallon. I set out on a cross-country trip, and every 200 miles I stopped and bought 10 more gallons of fuel. The fuel gauge kept going down, and after 1000 miles, it only showed 1/2 tank after adding fuel. At 1800 miles the engine almost quit at the fuel pumps, but I got going again. At 1900 miles the engine quit for good, and left me by the side of the road. My gauge showed zero. What is my problem?
The answer is the fuel usage exceeded the fuel replacement. The solution is to put more fuel into storage. You don't need to be a calculus professor to match a battery charger to an electrical system. It just needs to provide more electricity than you use, and shut down or throttle back once the battery is full.