Battery advise

[dpetersen]

Hey fellas after some battery advise!

I have a red arc sbi12 under the bonnet, charging a 105ah all rounder battery. I think it is around 650cca. It runs my fridge and all my other 12volt accessories, lights etc. Its also linked that I can jump start myself if my main is flat or if I need more grunt when winching. Battery is around six months old.

Now, iv just purchased a watersnake 54 pound electric motor for my tinny and need a new battery. It’s recommend to get a 105ah battery.
I’m looking at the century mrv70, deep cycle which is around $220.

My question is, am I better off putting the new century battery under the bonnet as it’ll get used more than the boat motor or keep it as it.
How do the century batteries go if they are need to jump start the car?

Cheers guys.


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[Cuppa]

How do you plan to recharge the tinny battery?

My choice for the tinny battery would be an AGM battery based on safety of a battery which will regularly be moved around & used sporadically. No chance of acid spills & can happily be left for a lot longer when not in use without recharging. A wet battery it will need recharging/topping up every few weeks if you want it to last. With an AGM if you recharge it after use on a smart (multi stage) charger to 100%, you can safely leave it for 3 months & no topping up required. If you did this you would get a far longer life out of it than the one you have in your car.

[dpetersen]

Thanks Cuppa. At the moment I have a century 12 amp 9 stage charger I was going to use for recharging it.
I love the idea of the agm, especially as far as safety goes. How long does an agm roughly last? I know out of my all rounder I only got about two years before it was buggered.
The only thing putting me off the agm is the price at the moment. Usually I’d be all for it but I bought my first house last weekend and have just signed my mortgage papers haha.
Am I right in saying (very roughly) it’s around $220 vs about $380 for wet/agm in the 105ah range?


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[Cuppa]

Thanks Cuppa. At the moment I have a century 12 amp 9 stage charger I was going to use for recharging it.
I love the idea of the agm, especially as far as safety goes. How long does an agm roughly last? I know out of my all rounder I only got about two years before it was buggered.
The only thing putting me off the agm is the price at the moment. Usually I’d be all for it but I bought my first house last weekend and have just signed my mortgage papers haha.
Am I right in saying (very roughly) it’s around $220 vs about $380 for wet/agm in the 105ah range?


I think you will get an AGM for a fair bit less than that. I just did a quick Google Eg. Giant 110Ah @ $299. with free delivery. (Look around more & ask locally too, this was just a 30 sec Google, so you may well get cheaper) https://www.aussiebatteries.com.au/batteries/deep-cycle-agm/110ah-12v-agm-deep-cycle-battery

A better known quality brand like Ritar I saw for under $320 for 100Ah.

Weight is a good indicator of quality. Ritar 100Ah are 29kg .My 120Ah Ritars are 35kg each. The Giant ones in the link are 110AH & 28kg. I'd guess they would actually be closer to 100Ah than 110Ah, but that's ok if it suits.

The difference in lifespan between a battery properly charged by a multi stage charger like you have compared to one charged by the vehicle's alternator via a solenoid (Like the SBi12) will be chalk & cheese. (Which is why I consider dc to dc chargers to be superior as they too are smart chargers). The AGMs have a far lower self discharge rate so can sit without use for longer periods, provided you recharge them before leaving them (no lead based battery likes sitting discharged for any longer than necessary - that is the main cause of shortened lifespan). If you get an AGM, & recharge it on your charger asap after each use you will be able to then disconnect it from the charger & 2 or 3 months later it's rested voltage will only be marginally less than full charge. Used like this it should give you 6 to 10 years. (My AGM's are currently 8.5 years, & previous ones I had were still in service at 12.5 years). Lifespan also depends on how much use they get too of course , but 6 to 10 years is based on the assumption the boat wont be used more than weekly at most. So whilst a bit more expensive to buy they are far cheaper in the long run if 'looked after', & the looking after is far less than with wet batteries.

[dpetersen]

Thanks for the good advice Cuppa, especially with the weights in destinguishing on a good battery, I didn’t know that.
I ended up getting another 105ah second hand off a mate for a box of beer. It’s been in his car about a year with no troubles and his just upgraded to an agm, so it should suit me well for a year or so until I can upgrade.


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[threedogs]

You could also trickle feed it to stay busy when not in use