Originally Posted by HorseThief
TL;DR - always store sealed lead acid batteries fully charged (13.0v or higher resting voltage), and for long-term storage (up to 3-4 months) disconnect from load (in your case make sure the unit isn't running (duh) and disconnect from the charger (read below for explanation of why). In your case charge 18-24 hours (48hrs max with unregulated power supply)
For sealed lead acid batteries, I do not recommend leaving them plugged into charger, especially if they are black and Decker. The batteries should be fully charged for 18-24 hours and then left unplugged for the winter - store indoors our outside, as long as the battery is fully charged no damage will occur from the cold - the rate of self discharge will actually be lower (though so will their effective capacity, so make sure there is no load hooked up (more general lead acid battery advice than your specific application)
Some of black and Decker SLA battery powered tools came with decent regulated power supplies that max out around 13.8 volts (measured at battery terminals, after current limiting resistor and blocking diodes)under load - this will not overcharge the battery. HOWEVER, I have seen a lot more unregulated power supplies being used that would actually peek up to about 14.5V (or higher) on a FULLY charged new battery - this added voltage will destroy an SLA much faster. Otherwise I have seen black and decker power supplies put out as high as 19v open circuit voltage (though considerably lower - 14.5ish) under actual load
It sounds like your units use a regulated supply for the charger, otherwise that battery would have been cooked in the much more average 2-5 years. Still I would recommend fully charging and then taking off the charger for seasonal storage.
My experience with these units is somewhat limited - I've mostly replaced batteries on the tube shaped sweeper/blower, with the occasional trimmer.
As far as the brand of battery or quality is concerned - I havent seen many AJC brand batteries out there, but I don't remember them being on my garbage list. The best battery I have found for the price point (as far as general purpose /non-application-optimed SLA) lately has been Powersonic, otherwise Enersys or Yuasa for average longest service life (depending on source/freshness) and lowest defect rate. Everything is built to a pricepoint - as long as you're not buying the cheapest batteries (lookin at you, Sigmastek!) off of eBay/Amazon or (shudder) Batteysharks, you're usually okay. I have seen plenty of counterfeit sealed lead acid and powersport batteries purchased online - usually coming in as scrap for recycling. Most of the time you can tell immediately by how much lighter they are then the battery they're replacing and inside I've found materials as cheap as polyfill (or some similar substance) taking up the bottom half of the battery with only half-length lead plates (gonna have to dig up my old work camera and find some pics)
Keep in mind everything is built to a price point, especially batteries. The original equipment battery could have been a very high quality extended life version with better cell separators and other more costly improvements. When the manufacturer can buy 100,000 batteries at a time, the cost difference becomes a lot less and they can afford to use a superior product - trying to find a TRULY equivalent replacement can become a costly, time consuming, and sometimes fruitless endeavor. Perfect example of this is portable car jumpstarters - you can get a GENERAL PURPOSE/deep cycle battery that is the equivalent or higher capacity, but it's not built the same way as the original that is optimized for high current output and even has thicker battery terminals or
Phew! 3 phone calls and one overly-long response to a simple question (and 1 ½ hours with the engine idling...) and now I can finally back out of my parking space and leave work.
Thanks for taking the time to write all that, HorseThief.
I will ensure they get a good charge and will unplug them sometime tomorrow night and forget about them until the spring.
