Battery Tender Amps ?

[Krats]

Hi all, I have a two bank battery system and want to install a battery tender. Seems like I can go from about 4 amps up to somewhere around 15 or 20 amps. Any advice on choosing the correct amperage?

 

[ZGhost]

It depends how fast you want your battery charged and ready for next outing. Higher amps, faster charge.
if you want to charge after a full day on the lake and go out next day, then 10 amp is plenty juice for the job.

 

[white2kstang]

I'm running a 2 bank 12amp prosport unit.

 

[ZGhost]

I’m running a Minn Kota 3 banks (only 2 banks used at the moment), 10 amps for two full size batteries and plenty of juice there.

Minn Kota Precision On-Board Charger Amazon.com : Minn Kota Precision On-Board Charger : Sports & Outdoors

 

[grywlfbg]

Yep, all about turnaround time. I just have a 4A unit, Noco Genius Mini. But we almost never go out 2 days in a row.

You can do the math for yourself. You just divide the Ah rating of the battery by the Amp rating of the charger. This assumes the battery is dead, which it won't be, so is really a worst case scenario.

That being said, I just tried to find the Ah rating of my battery (boat is in the slip but after digging around on the web I believe it is an Interstate 24M-XHD). On Interstate's website, they don't list Ah capacity but they do list Reserve Capacity at 25A.

Interstate Batteries - Product Detail

www.interstatebatteries.com

That battery is listed as 135 mins @ 25A. 135 mins is 2.25 hours. 2.25 hours x 25A = 56.25 Ah. So a 4A charger will recharge that battery in 14 hours. An 8A charger will do it in 7 hours.

 

[Krats]

Thanks for all of the feedback, it's very helpful

 

[marcham]

8A unit here ( prosport hd 8A dual bank), split amongst 2 batteries. How do you use your batteries? Is the charger strictly for a maintenance charge or do you have a large amp running all day without the engine running? Typically 10% of the battery 20hr rate is the right charger size. 80 Amp-hr battery: 8A charger. 5% is fine for a maintenance charger.The numbers above are for flooded cells. AGM batteries can take higher current.

I only plug it in if I'm not boating for 3 weeks or more. Remember to check the battery water level if leaving the charger plugged in for extended periods.