Battery / External display issues - any thoughts?

Hi,

I've got an '09 17" Macbook Pro running the latest version of Lion. About three months ago, the machine started switching off unexpectedly when <50% charged; the 'Service battery' error appeared, and sure enough on a trip to the Apple store the laptop failed the battery test. The battery had completed just 98 cycles; I wasn't the first owner but for the last year I have properly cycled the battery fully (100% down to 'reserve power') but since it got only an hour or two's use at a time per day it was charged once-twice per week and used 50 complete charging cycles in a year; I explained this but was told that it 'must have been used wrongly or been kept on the charger all the time'. The quote was a ridiculous £150 for a new battery and I was told the laptop is out of warranty anyway. Given that the cost of a 17" MBP is not far off that of a used car, I was rather shocked at the quality of service provided...

Less than impressed with Apple's alledgedly brilliant customer service, I decided to DIY (after all, there was no warranty to 'void'). On examining the battery, the old battery had clearly failed: there was expansion of one of its compartments and cracks to the plastic casing of the battery (I have kept the battery). Fortunately there appeared to be no external damage to the laptop casing or other components. Due to Apple's failure to provide a user-serviceable part (which is ridiculous since this is a part that anyone who can hold a screwdriver and insert a plug is capable of performing) I had to purchase a non-original replacement.


Battery life now is nearly perfect. I say nearly as I have noticed an odd behaviour which I don't know whether it was present before or not. If I use the laptop 'normally' all is well - it charges and discharges correctly. If however I wake the laptop with an external display plugged in (I have a mini-DP to 15-pin adaptor), the laptop has a tendency to 'forget' that the battery is charged. It reports (via the menu bar and also with Coconut, which show consistent values) that the battery has only a tiny fraction of charge. However, if you charge it for the expected amount of time to replenish the battery it recovers (ie. if it was at 95%, and you plug in the external display and wake the laptop it claims the battery is at 0%. However, charge it for the time taken to replete the last 5% and it acknowledges a full battery again). There is no service battery error and battery usage is linear. SMC reset doesn't help. SMC firmware is 1.43.


Any thoughts? This doesn't sound like a hardware issue to me - the battery itself seems to be behaving fine. Is this some odd error from the battery failing to always report the correct voltages (is this from logic based on the battery, or is establishing the correct amount of charge done from the logic board?) Or is it an SMC firmware / Lion bug? Has anyone else seen this kind of behaviour on other laptops? It's a workaroundable problem, but one I would like to solve if possible.

I'm not prepared to pay Apple for either a replacement battery (since the last one was clearly not fit for purpose, and doing so may not solve the problem anyway), and certainly wouldn't pay to replace the logic board if this was a logic board issue (since they cost nearly the same as a laptop in themselves and the issue is non-fatal). Does anyone have any sensible suggestions?