1L243 wrote:
Adding to, will be running parallel to the original battery. I thought it would be a good ideal to try and match the specifications of the first battery... But I will just find something similar in size....
Ah, Ok, there are many myths and half myths about multiple battery systems.
For example "All the batteries MUST BE IDENTICAL" ... Now...
If you are putting batteries in series, as one would do with a GC-2 (six volt 220 amp hour golf car battery) then the two batteries MUST BE IDENTICAL, ideally sequential serial number identical.. (But you need not be that obsessive) However if you have two pair, the second pair can be different from the first, so long as both batteries in THAT pair are identical.
There are many valid reasons for this.... But many apply series thinking to parallel batteries and this is where those reasons become Myth.
The Myth: If you hook two different batteries in parallel the smaller one will charge up first and signal the converter "Full Charge" and the larger one will never fill (True for batteries in series)
The Fact: The two batteries will form a perfect commune, the larger one will take the lion's share and the smaller one the rest of the charging current in direct purportion to their capacity, Thus both will reach full charge at EXACTLY the same time.
The related myth: When discharging the larger battery will supply more of the load and run down faster (half true)
The larger battery WILL provide more of the power, again in direct purportion to size, and both will run down at EXACTLY THE SAME SPEED in terms of state of charge.
WHY is this?
State of charge determines voltage, The lower the battery's voltage the more of the charge current it will suck up. when charging so they (After the first cycle) will be in perfect lock step.
Likewise the higher state of charge battery, thus higher voltage, will provide all teh current till it runs down to the other battery, so again after the first charge/discharge they are in perfect lock step.
The danger: If you have a really BIG battery (Say a 4D) and a very small (Say Group 24) in parallel and the smaller one shorts a cell.. It may go BOOM (well POP) spraying acid all over the place cause the larger battery will try to charge it, faster than it should be charged. But that kind of pairing is kind of rare.
