Battery Question

[Ryanm51981]

At the end of last year I was noticing a significant voltage drop when using my bow thruster and the thruster didn’t seem to have the ooomfff it once had . This is my 3rd season with the boat and it came with 4 Intimidator AGM 8a31dtm batteries . Previous owner bought them about two to three seasons prior to me buying the boat .
My question is how long do these batteries typically last ? I don’t know much about them other then that they are more expensive then typical batteries and supposed to last longer .
What batteries are powering my bow thruster on a 2006 380 Sundancer?
Should I purchase these again or are they not worth the extra money ? Any input is greatly appreciated.

 

[bobeast]

Properly maintained, a quality AGM can last 7 to 10 years. Most, are not properly maintained. For example, while you can charge AGMs using a dumb charger designed for wet batteries, they won't last near as long as when maintained with a smart charger which has charge profiles specifically designed for AGMs.

The second issue is deep discharge cycles. Batteries that are regularly discharged to within an inch of their life will not last near as long as those which are not. Single-purpose (deep-cycle) AGMs can regularly withstand 80% discharge cycles (wet cells ~50%). Anything more and their life will be seriously shortened.

Those 8a31dtm are dual purpose batteries meaning they can be used for starting AND deep discharge, which of course means performance compromises have to be made. Ideally, you wouldn't use dual-purpose batteries to drive your thrusters. They'ed be better served by deep-cycle AGMs which are not used or designed for engine starting.

 

[MonacoMike]

When I sold the boat mine were 9 years old and still strong. They were only deep discharged a few time and were on a quality charger year round.

MM

 

[tdschafer]

I had switched to AGMs a few years back & were not impressed with them. I even changed the settings on my charger for the AGM's but they lasted no longer than the previous wet cells. My experiment was one & done. Went back to wet cells.

 

[electricaldoctor]

Is one of these batteries dedicated to your bow thruster? Is one of them for staring the engines? Are the other two set up for your house loads? Please have a look to see how your 4 batteries are set up. To get a baseline for the general health of your batteries, you should disconnect them after you have them charged up and load test them individually.