Need help with 24V system and Minnkota charger

[Old Crow]

I recently purchased a 17? aluminum fishing boat with a 65lb Minnkota trolling motor that runs on 24V. System has a Minnkota MK220 (10amp/2 bank) onboard charger.

One of the batteries has died and am thinking of replacing it with an Optima Blue Top D31M
The second battery is about 2 years old and is not an Optima.
Will this older battery damage or decease the life of the Optima battery if I chose to buy one?

I asked this question to Optima and this is answer I got:

"The important thing to remember is that the charging voltage must be within the limits suggested by OPTIMA Batteries. If you are using an OPTIMA and a conventional battery, your system must charge each battery independently. Some isolators cause a voltage drop, so make sure your charging voltage AT THE BATTERY is sufficient.
Continued undercharging of a battery will lead to premature failure and a drop in capacity.
If you don't use an isolator then both batteries must be the same size, type, and age."

If I understand the charger correctly it is two separate chargers built into one.

Question is will the Optima (or any good marine battery) be short lived if only one battery is replaced in a 24v system?

 

[fishrdan]

Re: Need help with 24V system and Minnkota charger

Your Minn Kota charger will (check instructions) charge the batteries independently. Also, check the instructions and see how the "Battery Type" is selected on the charger. My 3 bank Minn Kota only allows you to select 1 type (flooded, AMG, gel) for all 3 banks, so mixing battery types will not be optimal for charging, wrong charging profile...

1 dead (bad/marginal) battery in a 24V series bank will not affect the other battery and cause it to go bad, but will affect the output of the 24V bank.

Personally, I would go with 1 type of battery, be it flooded, AGM or gel.

Also, 2 new flooded batteries could perform better than a 2 year old flooded battery and a new Optima, depends on the condition of the old battery.

 

[Old Crow]

Re: Need help with 24V system and Minnkota charger

Going thru the owner's manual I see this charger is for "charging and maintaining Flooded/Wet Cell, Maintenance Free and Starved Electrolyte (AGM) batteries only"

I see nothing in the manual about selecting battery types or mixing battery types or is there any selector on the charger itself

 

[Silvertip]

Re: Need help with 24V system and Minnkota charger

The charger will work fine. The 24 volt system operates best if both batteries have the same capacity and are of the same type. Don't know how much your Optima battery will cost you but about two hours ago I was at Sam's Club and they have a group 27 deep cycle with 180 reserve minute capacity and a three year warranty for $69.00. I've used their batteries in previous boats without complaint of any kind. I have a hunch you can get two (or three) new standard deep cycles for the price of one Optima. Unless you have a thick wallet, I see no reason to spend two and three times as much money for a battery that may or may not last two or three times as long as a good old standard deep cycle that is cared for properly.

 

[fishrdan]

Re: Need help with 24V system and Minnkota charger

No selector on charger, no problem, just use it. Not all chargers have the selector.

I agree with ST on the Sams Club batteries, I just bought 2- group 29's for $171 out the door. (BTW don't buy marine batteries from WalMart, no warranty)

To your original question, I have used 1 old and 1 new battery in a 24V bank and it's not great, you are limited to the performance of the worst battery.