Agm Batteries

[Guest fishrunner]

Hi all,

Just a question, you see I have a minnkota rt55ap powered by an AGM 100 AH deep cycle battery. Now I'm wondering how long you would expect these absorbed glass matt batteries to last?

I've had this battery for about 18 months and worked a treat up untill about a month ago,- I originally was like,- this battery will last all weekend with wise use, but now seems to go flat in about 6 hrs.

The battery has always been charged back up with an automatic charger that tappers off the amps as battery reaches full charge. Batteries use has been pretty heavy - close to flat at the end of the day.

Does anyone have experience with this type of battery, and if so how have you found it? Also what about maintenance free batteries? went for a agm battery originally as I liked the idea of it's toughness and not worried if it fell over(it never did). But now that I'm looking at having to get a replacement I don't want to have to spend another $280 for a battery that will only last round 18 months!!!

Have I mistreated this battery in some way?

thanks

[wakd]

The cheaper AGM batteries usuually state they have a life of around 5 years, more expensive ones have a 10 year life. The batteries life is really based on cycles though (discharge, recharge cycles), and different brand/AH batteries have varying amounts of cycles before they give up the ghost. If yours is going after 18 months, it could be that it is an inferior quality battery (no offence, but $280 is a cheapish 100AH AGM battery), but more likely it is to do with how you charge it. You should be using a good 3-stage "smart" charger, which it sounds like you are, but you must try to get the battery back onto charge as soon as possible after it has run down. Leaving an AGM battery dead for a few days reduces its life. I always put my battery (which is a calcium maintenance free, not an AGM, but same principle applies) onto charge after every outing, regardless of whether it is run down much or not. If you have been only recharging the night before going out again (ie a week after running it down), this would be your problem.

HTH,

Ben

Edited November 22, 2005 by wakd

[zook2001]

Totally flattening a battery is not a good idea if you can help it and will basically halve you battery life compared to only 50% discharging. You would still hope for maybe 150 to 300 cycles if it’s a really good battery with a decent charger.

I’m on my second year with cheap wet cells but I have two and try to keep to 50% discharge.

Regards Charlie

[Guest fishrunner]

Thanks for the info guys,

I'm gonna go over all the terminals and clean them all up, did a test and had 13.8 volts , which I believe is fully charged will take another reading in a few days to make sure it's holding charge.

Then for another test run and see how it goes, hopefuly well.

I would like to keep it above %40 charge, though sometimes it's not easy with every snag/stretch looking worthy of another cast,

Will see how we go.

cheers

[pogo]

13.8 sounds high, how long had it been off the charger?

A good way to test it is to test it under load, charge it up, take it out for a fish and check what the voltage is as it sits in the boat then run the MK flat chat, should draw about 40-45 Amps and check the voltage again under load to see what sort of voltage drop you are getting,

I've only ever done this by disconnecting the ignition leads on a petrol motor and running the starter, I dont know if the maximiser will spin out your multimeter

From the 12V bible for boats

Battery at rest, gretaer than 12.6v 100%, 12.4v 75%, 12.2 v 50%, 12.0v 25%, 11.7 or less flat battery

Under starter motor load if the voltage drops to less than 9.6v the battery is due for replacement.

How many cycles do you reckon you have got out of the battery, they should be good for at least 200 and some of the better ones will exceed 300 and thats supposed to be fully charged to flat (11.7v)

Edited November 23, 2005 by pogo

[wakd]

With regard to discharge, its true regular lead acid batteries designed for cranking should not be discharged too low - around 75-80% is the number I have seen quoted. Deep cycle batteries on the other hand are designed to be, err, deep cycled - in other words run close to flat, and then recharged. Numbers I have seen quoted on AGM deep cycle batteries have been cycles in the thousands, I'll double check the numbers I have tomorrow and let you know...

[zook2001]

With regard to discharge, its true regular lead acid batteries designed for cranking should not be discharged too low - around 75-80% is the number I have seen quoted. Deep cycle batteries on the other hand are designed to be, err, deep cycled - in other words run close to flat, and then recharged. Numbers I have seen quoted on AGM deep cycle batteries have been cycles in the thousands, I'll double check the numbers I have tomorrow and let you know...

Gotta disagree mate every single battery maker state the deeper the discharge the shorter the life,mind you you also need to factor in the extra cost and weight of doubling your batttery size.Three hundred or more cyles is quite allright for the weekend angler.

Regards Charlie

[Guest fishrunner]

hi all, , voltage had dropped from 13.8 to 13.29 over 7days, now I've disconnected the circuit breaker and recharged the battery again to see if it still drops any charge at all,.

for a bit of interest,- here's a link to my battery spec page!,

http://www.absorbedpower.com/battery/pdf/A...00C-01Sep05.pdf

will keep experimenting and testing, trying to solve this lil problem.

I've also removed kota prop to check for any form of extra resistance, but alas nothing was there, will see how we go, will keep you informed

cheers