Faulty Alternator

Are both 12V batteries (connected in series to give 24V) showing the same problem?

Try swapping the suspect batteries with similar batteries that are working (assuming you have more than one gas engine).

If the swapped working batteries start to show increased water usage you know it's likely the alternator or something connected to it, if the problem moves with the batteries or only one of the series connected batteries has a problem you know you likely have a battery failure and can just replace the battery(s).

Is it a 12V alternator? 24V alternator? 48 V alternator?

What V is it putting out?

How is it connected?

How are the batteries connected?

How do you expect anybody to help?

use this

The voltage regulator for the alternator if faulty causing the battery to overcharge. This causes the electrolyte to boil.The replacement alternator probably has a faulty voltage built into it. Try a new alternator.

I agree it's likely to be a faulty voltage regulator, but OP didn't say it's a replacement alternator. "Batteries water make up has increased...." suggests it worked OK before the problem arose.

He should measure the voltage, if it's much above 28 volt there's a problem. He didn't say what type of voltage regulator, if it's an old electromechanical (vibrating contact) type it should be possible to adjust it. If it's electronic it's likely to need a replacement regulator.

Do you know how to read a volt and am meter? If you can't do basic electrical troubleshooting then you really need to find somebody who can.

Those batteries will fail very soon, if they haven't done already....assuming the charging is too high as would appear.....

A cheap charger will cause the same problems, as will a defective charger.....or no charger!!!

Give details of your charging control please?