"Truck batteries only last a year" is my mechanic lying to me?

Fail as in shorted cell, or fail as in worn out?

My truck was owned by the military before, and I dont think they would settle for substandard batteries. The batteries are not Freightliner original. Right now I am unable to check what brand it is.

 

I have not heard about different lead acid batteries requiring different charging profiles, and I have designed battery chargers for a living. Do you want to support that with a source? Sounds like something a seller of snake oil would want to have people believe.

AGM means "absorbant glass mat" and it is basically a method of preventing leaks and to allow designing the battery to be sealed (no vent hose, for vehicles that have that). It provides some marginal benefits but AGM or not, it is still a lead acid battery.

(I am assuming you are charging your batteries with either the vehicles alternator(s), or a charger made for lead-acid batteries - not with some random 20+ volt cable out of somewhere...)

 

No it doesnt.
I dont know how the truck was used before me, but it does have ShorePower.
It was recently parked for four months and after that it started immediately, and as far as I know they have not been charging it for me... That was three months ago and now all of a sudden it cant handle two days without losing charge. That tells me it must be a cell short in one of them. Or a parasitic draw, but the main power switch has been turned off so I assume it couldnt be that?
Oh well, I will take back the old batteries and after charging them I will perform a condition test on them.

 

Ok... What is it that taxis do differently? As long as the charging regulator is proving the battery with the correct charging voltage, I would have thought that they enjoy being in a car which is driving almost constantly...

I know the biggest battery killer is heat though. I live in Las Vegas where temperature gets over 110 F (more inside of an engine room I would assume), and I had a battery in one of my cars go bad in less than three years. While the batter(ies) in my Mercedes lasted 8 years. I think it is peak heat that kills batteries, like a day at the pool when your smartphone gives a temperature alert. I have found that every time after that happens the measured battery health is reduced.