24V or 2 X 12V for D2 Direct Electric Starter?

I have a 24v charger on my 2-12V batteries on my loader---there are many 24v chargers available from $50 to $100 range---i use to charge one 12v at a time-but never disconnected cables--just put + to + and - to - on each battery with the 12v charger leads

Never seen a 24 volt battery for sale so I question trying to go down that road. Traditionally 24 volt systems have either two 12 volts 7nnseries or even four 6 volts. I think the 6 volt setups were more popular 40 years ago than now.

If you can fit them in the space, group 31 batteries (used in most heavy trucks) are the cheapest and generally highest quality batteries available today. They are available with either traditional post terminals or stud terminals. I much prefer the stud terminals because making series or parallel connections is much easier. It is pretty simple to stack 2 or 3 ring terminals on the stud if needed. Also I can make cables with a hydraulic crimper I bought off ebay for less than $30. Before I got that one I had made a crimper out of an old broken bolt cutter by grinding the jaws.

If you want to charge a set of 12 volt batteries connected in series, as mentioned already, there is no need to disconnect the cables. Just match positive and negative 12 volt charger leads to the corresponding battery terminals. If the connections you need are not accessible you could run smaller wires out to a plug that has the correct polarity to make your connections for charging.

Any time you have multiple batteries you will find that one lasts longer than the other. Even in parallel connections, though one shorted battery will discharge all of the others, if you separate them and charge individually you will usually find some are still somewhat usable. Eventually one shorted battery will ruin all those connected in parallel with it by sulfating the plates from being discharged all the time. In series connections you don't have the problem of a shorted battery discharging the other battery but you do have problems resulting from uneven charging that results when you apply the correct series voltage to a string with bad batteries included.

For best life of any multiple battery "banks", it is always best to replace all of them with identical batteries at the same time. This usually results in some "good used" batteries being left over. I make use of these in other vehicles that use only a single battery or group them in banks of similar age and type.

You could always charge from the tractor with a 24v gen, or a 12v & series/parallel switch.

Thanks for all the input on my question. Sounds like finding 2 new 12V batteries to fit within the space is the best way to go.

I still have a question on the charger. My electrical ignorance is vast, but the batteries are connected in series (+ to -, - to +), so the overall output is 24V. If I simply hook a battery charger up to the + and - of the nearest battery, why wouldn't I need a 24V charger?

Thanks for all the input on my question. Sounds like finding 2 new 12V batteries to fit within the space is the best way to go.

I still have a question on the charger. My electrical ignorance is vast, but the batteries are connected in series (+ to -, - to +), so the overall output is 24V. If I simply hook a battery charger up to the + and - of the nearest battery, why wouldn't I need a 24V charger?