[Feat] More accurate battery measurement

[vicgwee]

Battery state of charge estimation #43 is not accurate, it drops by 60% in the first 3 hours but the last 9% can last it 7 hours.

Solutions:

• Modify LIPO_DISCHARGE_CURVE based on these experimental values.
• Add a fixed voltage drop (200mV is factored in the "corrected" column)
• Replace the battery, perhaps ageing affected it.

Data Setup: 380 mAh battery and barometer connected Start time: 1035 hrs

Time	Measured %	mV	Corrected %
0	69	3948	95
1	46	3824	80
2	23	3742	69
3	9	3680	61
4	6	3625	47
5	4	3596	37
6	3	3547	25
7	2	3520	17
8	2	3488	10
9	1	3400	5
10	0	3100	1

The battery ended at 2445 mV at about 10.5 hrs

Data is here: debugLog00006.csv

[vicgwee]

Similar findings here: debugLog00007.csv

Will try implementing the voltage offset first