Last fall my TM batteries ran down after 5-6 hours of medium to heavy use. Previously they never ran down during a full day on the water. They were less than one year old. Put them on the charger and the next morning they were charged to about 12.6-12.8 volts but the specific gravity reading on all 12 cells were at the "discharged" or low levels. I've never had all cells at that low of a specific gravity after charging. I convinced Sams Club to replace the batteried and they have worked great for 5-6 months. We fished Fork in the wind Thursday and my TM batteries ran down after 6-7 hours. Came home charged them overnight and today they are reading 12.7 volts but the specific gravity is reading "discharged" on 11 and "fair" on one cell. I've had this boat for 4 years and this problem just started less than 6 months ago.

What would cause the batteries to develop the dead cells in all cells at the same time. In the past I've had car batteries fail but they normally have only one cell die.

Just a bad batch or run of Battery's. I have seen new battery's go bad in a week because of a bad cell. You also need to make sure your charger is charging correctly and that it is also set or made to charge the type of battery's you have. I went threw 4 moper factory battery's in 2 years under warranty. All because there battery's were cheap made.

what amperage is your charger charging at? if not at 13.8 or so then your charger is going out, fully charged battery should read 13+ volts, if you have another charger try it on one by itself and see what happens.

Voltage while charging is running about 14.5, soon after the charger turns off the voltage is around 13.5 and after sitting for several hours it is almost at 12.8.

I put a different single bank charger on one of the batteris last night and it is at 12.77 this morning but the specific gravity is not even registering on the hydrometer. TM spins up fine but i suspect that the battiers will not last long on the water. Checked my hydrometer on my truck battery and it shows that it is fully charged so I know the hydrometer works.

I will try to convince Sams that the batteries are bad again. These are Engerizers batteries which are the new 29 series Sams is carrying. They run just under $100 each.

I don't have anything but the trolling motor connected to these two batteries so it the problem has to be either the TM (Minn Kota 80 Maxxium), the batteries or the charger. Seems odd that I've had two set of fairly new batteries die at the same time, one battery OK but both at the same time makes me suspect the charger or TM.

I know you shouldn't totally discharge the lead-acid batteries but can you kill them totally by running them very low.

That is not correct information - a fully charged battery should have 12.67 volts at the battery terminals with NO LOAD on the batteries. The charger should build the voltage level to 14+ volts (I've seen 14.2 volts to 14.9 volts) before going into float mode or shutting down -- which it does depends on the brand/model of battery charger.

If you're seeing 13+ volts at your battery terminals, either the charger is still charging or it has gone into float mode.

Not uncommon for hydrometer tests to show a low state of charge after charging --- especially if the brand/model of charger does not bring the charging voltage to a high enough level. I've disposed of more than one charger because it was undercharging my batteries. These had a maximum charging voltage of 14.2 -14.3 volts. The charger I have now (Dual Pro) brings battery terminal voltage to 14.9 volts and when it shuts down a hydrometer test shows battery charge state to be 90% or above.

C.

My charger is also a Dual Pro sportsman SE which is a 10 amp per bank charger and it seems to behave properly, starting off with the 4 lights and around 14.5 volts at the terminals. I haven't watched it go through a cycle is years but it steps down as the battery voltage comes up and eventually gets to the green light and I will have around 12.7 volts. When I plug in in on a fully charged battery it will go through the cycle in a second or two and show green. I don't think I can salvage these batteries so I will watch the charger go through a cycle when I get the new batteries installed. Maybe it is starting off OK and then cycling down too fast and not getting them up to full charge.


Wonder if Boris Marine Electronics could shed any light on it. Replacing any of these components is too expensive to not be going after the right problem.

try popping your breaker, charge the batteries then check them 12 hrs later. this will tell you if you have a drain on the tm.

A fully charged battery will show 13+ volts immediately after unhooking the charger and will take a battery several hours to level out around 12.6 volts after charging.

Charger's voltages sound good. Batteries sound like they're killed, again.

One possibility if you have a a digital trolling motor:

The trolling motors selling now can run unnoticed, almost at full speed even though their flooded lead acid deep cycle batteries have been almost 100% discharged with their voltages dipping low and the lead plates quickly become irreversibly sulfated. Summer heat contributes to this issue. So does the wind you mentioned which causes us to drain TM batteries much quicker and further than typical.

After several cycles of the batteries being severely over 50% discharged, they will typically re-charge quickly but with absorbing little current, they will the next day again have little usable capacity. They are as you said "dead".

They may again require replacement and the replacement batteries may need to be bought with more reserve capacity minutes (RC). And their voltages need monitored during the day to ensure they are never overly discharged. Stop and recharge any battery falling to 12.3 volts.

Almost 200 RC minutes per battery may be needed on a windy day to ensure the battery is not overly discharged.