Can you mix bat­ter­ies?

Canal Boat - - Technical - MIKE PARRY, via email TONY REPLIES…

QI have just bought a re­place­ment starter bat­tery and have found a spot for it in a sep­a­rate bat­tery box so that I can up­grade to four leisure bat­ter­ies. I re­placed the leisure bat­ter­ies in June 2014 (Nu­max 100Ah) when the orig­i­nals failed. I know you shouldn’t mix old and new bat­ter­ies, but does ‘old’ just mean ‘dead’?

I have treated the new bat­ter­ies well so would it be wrong or cause a prob­lem to add one more (same brand/type) 18 months later? Or must I wait an­other three or four years until they need to be re­placed and then buy four?

AIf your ex­ist­ing leisure bat­ter­ies are in a good ser­vice­able con­di­tion, then adding an­other should be okay. Fit the new one and then run the en­gine to recharge the whole bank. Any more dis­charged bat­ter­ies will take a greater pro­por­tion of the avail­able charge, so over a day or so, they should all be charged to the same de­gree.

Good prac­tice says bat­ter­ies should al­ways be changed in whole sets and most pro­fes­sion­als will be very re­luc­tant to do other­wise. This is be­cause when (not if) an older bat­tery de­vel­ops an in­ter­nal short cir­cuit it will flat­ten the other bat­ter­ies in the bank. Then the newer bat­ter­ies will sul­phate, lose ca­pac­ity and will pos­si­bly be ru­ined.

It is def­i­nitely best not to mix bat­ter­ies with dif­fer­ent max­i­mum charg­ing volt­ages be­cause the charg­ing would have to be set to the low­est value and that would in­crease the time taken to charge the whole bank. With­out model num­bers, I ex­pect the Nu­max 100Ah bat­ter­ies are ei­ther AGMs or wet open cell bat­ter­ies so if you stick with the same type (not make) it should be fine. bat­ter­ies with han­dles, so if your en­gine bat­tery is in work­ing or­der, forget about it. Although it seems counter-in­tu­itive, the starter bat­tery has a very easy life and rarely gets any­thing but a light dis­charge un­less the en­gine is faulty. They will nor­mally be all-but fully recharged less than an hour after start­ing.

An on­line man­ual gives no data for the starter bat­tery size, but as long as it’s roughly the same size as your leisure bat­ter­ies with a ter­mi­nal lay­out that al­lows you to con­nect the leads, it will be fine. I would ex­pect it to have a CCA (Cold Crank­ing Amps) rat­ing of around 900 CCA and/or a min­i­mum Ah (Amp hour) ca­pac­ity of be­tween 80 and 90 Amps hours. This will prob­a­bly be overkill but it will fit next to the do­mes­tic bank and not re­quire the ad­di­tional pack­ing to com­ply with the Boat Safety In­spec­tion as a smaller bat­tery would. An on-line out­let lists one at £75.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.