Jump-start/tire-pump unit has issues

[Joel_BC]

A woman friend of the family has brought this unit to me to see if I can remedy its problem. Problem being, she’s found that the unit doesn’t pump her tires anymore — simply doesn’t start building any pressure within the unit.

To be specific, this is a Stanley 500 AMP, Jump Start System, model J5C09CA — a combination jump starter, battery charger, and compressor.

The lady says it was working for her within fairly recent months. She was keeping it plugged in, apparently over a long stretch (she thought this was a good idea, but I haven't seen the manual for it, and don’t know if this is recommended).

Neither the compressor nor the battery boost/charger function works when connected to 120v AC line current that is standard in our area. I attempted to test the charger function by connecting the unit to a battery of mine, a 12v-DC lawn-tractor battery. There seemed to be no juice going to the battery. BUT what did occur is that when I tried the compressor with the battery connected, it actually ran!

Without any reference to a manual, I just guessed that the compressor should operate by line current alone (and not be dependent on external battery power). I'm guessing the internal battery in the unit must be ruined. I have no experience opening one of these up, but I'm a generally handy guy — I weld, fix small engines, have wired a couple of shops, etc. With a little hand-holding, I might be able to fix this thing. THANKS.

[bdunham7]

Take it apart, there's probably an AGM battery in there about the size of the battery in a large UPS.  It probably is trickle-charged so it won't work on line power with a bad battery.  I suppose it is possible that the charger portion has failed, but the bad battery seems most likely.  Do you have a multimeter?

[Joel_BC]

I have a multi meter.

I'm a little nervous about loosening all the screws and taking the casing apart. Never having been inside one of these, I wonder if it's going to be tricky to put it back together. Can I suppose that because it's the venerable Stanley brand that it will be easy disassemble, easy re-assemble?

[bdunham7]

I'm a little nervous about loosening all the screws and taking the casing apart.

Sir, this is EEVBlog.  Get in there and get (un)screwing already! 

Besides, what do you have to lose?  It's junk otherwise and there aren't any Stanley repairmen that I know of.  And no, you can't depend on it to be anything other than a cheaply made pile of junk.  If it isn't that bad, then you can be pleasantly surprised.

[Ed.Kloonk]

To be specific, this is a Stanley 500 AMP, Jump Start System, model J5C09CA — a combination jump starter, battery charger, and compressor.

The lady says it was working for her within fairly recent months. She was keeping it plugged in, apparently over a long stretch (she thought this was a good idea, but I haven't seen the manual for it, and don’t know if this is recommended).

https://www.manualslib.com/manual/1685362/Stanley-J5c09.html

https://www.libble.eu/stanley-j5c09/online-manual-744411/

[TheMG]

The AGM lead-acid battery inside is most likely toast. Regardless how well it's taken care of, they have a limited usable life and eventually need to be replaced. The life of the battery is shortened if stored at high temperature (hot car parked in the sun), overcharged (manual does seem to indicate the built in AC charger will not permit overcharging so leaving it plugged in should be ok), or allowed to spend a significant amount of time in a partially discharged state.

Under ideal circumstances about 5 years would be the expected usable battery life (where it can still be used to jump-start a vehicle). This can be as short as a few months if the unit is abused (for instance, heavily discharged then allowed to sit around for a few weeks before being recharged).

The charger inside these things is usually quite small, whereas the air compressor inside likely requires somewhere around 10A to run (and more on startup), far in excess of what the charger is capable of, so it needs a healthy battery to work.