Another battery question...

[yachtShoestring]

I have two batteries on board, one main for the engine and one leisure battery. -it seems to charge of the alternator.

The main battery is physically larger and blows the fuse when I try to charge it, (6amp slow charger) the smaller one takes a charge but depletes quickly.

Should I be replacing both of them? Any advice?

many thanks!

 

[Wigeon]

Are they connected in series or parallel? I always pair my 2x 130 amps in series { i.e =-ve of one to positve of other, takeoff from unused +&- terminals
Still gives you 12 volts, but much bigger amph.
Both therefore charged by engine, and charge lasts forever. also my engine driven alternator seems to pump 14.5 volts into them every time I run the engive for a while, and then both batteries settle doen to 13.5 volts. Ive always found this system best, since on poor starting days, you have twice as long before the dreaded whir whir nothing!

 

[ccscott49]

If you connect the positive of one battery to the negative of the other, ie in series, if they are 12 volt batteries, and you connect to the twp spre terminals positive and negative, you will get 24 volts! at 130ah.

However if you connect negative to negative, positive to positive and then tap off negative and positive. ie paralel, you will have 12 volts at 260ah.

You have made a mistake in your post, or on the boat.

14.5 volts from the alternator on a 12volt system is normal.

 

[Peterduck]

With the main [starter] battery blowing a fuse, there must be a short-circuit somewhere. If there is none to be seen in the cabling, it is possible to have a short-circuit inside the battery, in which case it is a candidate for recycling. The house battery may be either not being charged enough [it can take a surprisingly long time to charge a battery fully] or it may be another candidate for recycling if it won't retain the charge that has been fed into it. Take it home and leave it on charge for two days at least, and then test it with your hydrometer. Test it again after a week just standing and see if it is still fully charged. If the level of charge drops significantly, the battery has passed its use-by date and will have to be recycled. Put a slab of styrene foam or other thermal insulation under the battery to prevent it getting 'cold feet'. This may sound strange, but if you don't believe me, ask any auto-electrician and they will confirm it. They are like girls, and have to be kept warm.
Peter.