My Portable just blew it's (new) battery. (M5120)

[ConventionalMemories]

 So, a few months ago I restored my Macintosh Portable m5120, (recapped logic board, repaired the HDD, and rebuild the battery).

This all worked out great and I had it running for a few days /charge cycles. As I went on to some of my other projects I put it away. 

Today I took it out again and it wouldn't boot. I took the battery out and it measured around 3.3v 

So I plugged everything back in and let it charge for a few hours.

About 6 hours later I tried to boot again and it booted right up. Everything worked great as expected.

After about two hours of use I noticed the back (above the battery) getting very hot. I turned my portable off and took the battery out. To my surprise the battery was very hot and completely swollen up (bulging on the sides). It also made a hissing sound, as if the acid on the inside was boiling. Luckily it didn't burst open. 

So now my question is, did I just have a defective battery? Or is my Portable to blame?

I checked the voltage that the Portable is putting out in the battery compartment, around 7.30-7.45V  (no battery installed)

it seems a bit high for a 6v battery?

Can anyone with a Portable confirm at what voltage it charges it's battery?

Could it maybe have been too much of a current draw for the battery? I do have the backlight upgrade installed, a modem, 2 ram expansion cards, and the original Connor hard drive. 

Also, I am using the original power adapter.

And the battery i was using is an "Ultracell UL4.5-6"

Any advice is very appreciated, thanks.

 

[IlikeTech]

Not sure why it failed, but those voltages look normal to me, as lead acid is normally higher nominally than the 6 volt label, and charge voltage a bit higher than that.

 

[Stephen_Usher]

Indeed, 7.5V is the correct charging voltage. If you check on the label on the battery you'll see this listed.

All I can suggest is that there's a fault in the battery generating an internal short, possibly buckled plates.

 

[ConventionalMemories]

Indeed, 7.5V is the correct charging voltage. If you check on the label on the battery you'll see this listed.

All I can suggest is that there's a fault in the battery generating an internal short, possibly buckled plates.

Thank you for confirming this, that's what I was hoping for. 

I guess I'll just order a new battery then, and hopefully it will all be fine again.

 

[techknight]

It could be a couple of things. I agree with everyone else, its probably a defective battery. 

If the hybrid doesnt shut off the charging circuitry, even then, the battery wouldnt do this. it would just burn off the excess charge as a little bit of heat. UPS's do this all the time.