It's been a grumpy couple of days.
I have a 13" laptop, used for work two days a week, which is suffering now from significant loss of battery life. It does not seem long, but looking back, it was new in 2016. A replacement is lower spec, and expensive, but may be inevitable.
A new battery was purchased. I duly worked out how to get the thing apart, removed the old battery, to find it has swelled a little, and plugged in the new one. Booted the laptop, "battery not fitted" it declared. Checked the connection, fine. Internet search suggested a procedure to empty any residual charge in any capacitors, by removing the battery, and holding the power button for a minute. (AC disconnected) No change, battery not recognised.
An email to the supplier got a prompt response, and they promised to trest one before sending. Replacement arrived. More faffing inside the machine, fired it up. This time, battery recognised, but showing 0%, but not charging. Left plugged in for 7 hours, no change.
I'd heard that lithium ion batteries do not like being fully discharged, often failing to recover. Had a similar problem with a repalcement phone battery a few years back, had to replace the phone instead. Another internet search confirmed that a dead or very low battery is probably scrap. Some recover if connected diretly to a charging current, by-passing the laptop control software. Whilst it is rated at 11.75v, I think my 4A car charger might not get the result I need. Intriguingly, the power supply to the laptop is 9v.
More internet searching, found a wiring diagram for the tiny multiplug. Three power connections. Original battery gave 11.1V. Both replacements show 6.5-6.7mV. That's less than one tenth of a volt. Unsurprising that the laptop cannot see them.
Supplier is in the middle of a warehouse move, so will request return in about "15-30 days". No mention of replace or refund, so I've asked for clarification.
Meanwhile, one hinge is breaking away from the plastic case. Haven't yet investigated a repair, but screws through from outside might work, although not pretty, but cheaper than £400-500 for an inferior replacement. No point fixing the hinge unless a good battery is available somewhere.
Meanwhile, I have to carry the 15.6" laptop, or revert to my very old, but very reliable 10" netbook. Seems a plan.