I have a 24 volt Ultrex trolling motor.  The last time I was fishing the motor seemed to lack its usual pep.  I got a digital battery tester and one of the batteries was at 10% health.  The other was 72%.  This is the 5th season I am using them.  Should I just replace them both?  Or is the one battery good for this season?

Replace both batteries so they are the same brand and age. The weak battery will drag down the stronger battery, weak link in the chain!

Make sure you clean the battery posts and terminals then retest under load.
Tom

PS, Harbor Freight has a good inexpensive battery load tester on sale this weekend.
 

I would just replace them.  If they are wet cell then you have definitely gotten your money's worth.  If they are AGMs, I would have liked to have seen you gotten a couple more years out of them but 5 years isn't that bad.  

Get 2 new batteries with the same reserve capacity.

1. Buy a couple of 50 or 60ah lithium LiFePO4 and never have to replace them if you're older than 60.

Always replace both at the same time.

 

5 years is a good run if they are lead acids

I've got 6 good years out of mine on my Tracker.  They are getting replaced this winter when the hard water season arrives.

 

Toying with going to lithium.  All add one lithiumfor sure as a house battery, but might just stay with lead acids for the troller for boat balance reasons.

 

On 6/13/2025 at 9:31 PM, RobA said:

I have a 24 volt Ultrex trolling motor.  The last time I was fishing the motor seemed to lack its usual pep.  I got a digital battery tester and one of the batteries was at 10% health.  The other was 72%.  This is the 5th season I am using them.  Should I just replace them both?  Or is the one battery good for this season?

 

You could do just one if you had to.  It would work and get you through the season.  It isn’t the best long term choice since the well used one would drag down the less used one over time.  If you had a half decent used battery sitting around then I might do that to get through the season, otherwise just get a new set.

 

16 hours ago, slowworm said:

I've got 6 good years out of mine on my Tracker.  They are getting replaced this winter when the hard water season arrives.

 

Toying with going to lithium.  All add one lithiumfor sure as a house battery, but might just stay with lead acids for the troller for boat balance reasons.

 

 

I went lithium when i built my boat (had lithiums in the kayak before it).  I went with 1 24 volt for the motor and a 100 ah for the electronics.  I kept a lead acid for the cranking battery.  To do it again I would have gone 2x12v for the motor since charger options are tough for a 24v bank and 2 12 v banks in the same charger.  Other than that, I have no regrets whatsoever with lithium and wouldn’t ever go lead.  If you need weight for balance, still get lithium and put two sand bags in to make up the difference. The consistent voltage from lithium is so nice.  

When lithium LiFeP04 came out a decade ago they were expensive and offer 1/2 the weight and 2X the battery life then AGM’s. Down besides cost was new onboard charger was needed and questionable cranking power.

Today a new technology has arrived Marine Solid State batteries offering 1/2 the weight of LiFeP04 lithium batteries, no fire, 2X the runtime of lithium batteries plus longer life! Down is cost! Sound familiar!

Tom

18 minutes ago, WRB-2.0 said:

no fire

Lithium-Ions are the ones that catch fire readily, Tom - LiFePo4 batteries are considered 'incombustible'. Drop them in a fire, smash them with ton+ weights, shot a magnum round through them....all you'll do is make them unusable....they won't catch fire.

 

EV's still have issues with fires cause the majority of the batteries they use are Lithium-Ion, not LiFePo4.

I'm a believer in LifePo4 batteries and I believe they are much safer than Lithium-Ion batteries but I think some are going to far in say they are completely safe.  If punctured they will get very hot and release toxic gas.  The extreme heat can cause other things in the boat to catch fire.

 

 

7 minutes ago, Tennessee Boy said:

The extreme heat can cause other things in the boat to catch fire.

Not always, but if it does happen, the fire caused by this can be put out with a standard Class ABC extinguisher - which every boat should have instantly accessible.

 

A Lithium-Ion fire would need a Class D extinguisher to put it out as the metal itself is burning.

Just repeating the Solid State statement of facts “no fire”. Good for boaters.

Do kayaks carry fire extinguishers, most have lithium batteries to save weight. 
Tom

PS, happy farther day👍

32 minutes ago, WRB-2.0 said:

Do kayaks carry fire extinguishers, most have lithium batteries to save weight. 

I dunno - but I carried one in my canoe and I had an AGM for my TM and electronics.

1 hour ago, MN Fisher said:

Not always, but if it does happen, the fire caused by this can be put out with a standard Class ABC extinguisher - which every boat should have instantly accessible.

 

A Lithium-Ion fire would need a Class D extinguisher to put it out as the metal itself is burning.

Did you watch the video?  The guy poured a 5 gallon bucket full of water on the battery and it kept burning.  What he did to set the batteries off was extreme.  Anytime you have that much energy stored in a small space there is a chance for things to go wrong.   Same is true with lead acid batteries.  I have lithium batteries and I not concerned but if something did puncture one of the cell it could be bad.  My batteries are right next to my fuel tank.  If one of mine starts burning,  I'm not gonna try to put it out with a fire extinguisher,  I'll be going swimming.