More on Battery Life

After a week of use, a few statistics can be developed regarding the average use of the iPad and its battery capacity during archaeological excavation.  Table 1 below identifies my tracking of the battery life used each day for the ten iPads. iPads 5, 9 and 10 were only used for the cemetery survey work which only occurred on Thursday and Friday last week.  In addition, Friday afternoon (7/12) was truncated by a lecture and the water screening demonstration so only represent about a 5-hour day.  Due to a glitch, iPads 1 and 2 were not charged the night of 7/9/2013 and the students started 50x50-cm shovel tests (with traditional paper forms) the morning of 7/10/2013 while the units were charging.  iPad 4 was at 8% at 1 pm on 7/10/2013 when it was recharged, therefore only representing about a 4.5 hour work day.

TABLE 1. iPad BATTERY LIFE USED OVER A FIVE-DAY FIELD TEST IN JULY

	7/9/2013			7/10/2013
iPad#	Start	End	Battery Life Used	Start	End	Battery Life Used
1	78	42	36	100	45	55
2	68	3	65	100	84	16
3	100	86	14	86	75	11
4	100	61	39	61	8	53
5	100	100	0	100	100	0
6	81	56	25	100	55	45
7	76	55	21	100	100	0
8	100	59	41	100	67	33
9	100	100	0	100	100	0
10	100	100	0	100	100	0
	7/11/2013			7/12/2013
iPad#	Start	End	Battery Life Used	Start	End	Battery Life Used
1	100	73	27	100	97	3
2	100	50	50	100	79	21
3	100	93	7	100	100	0
4	100	42	58	100	82	18
5	99	24	75	100	37	63
6	100	60	40	100	88	12
7	100	37	63	100	50	50
8	100	68	32	100	48	52
9	100	14	86	100	41	59
10	99	22	77	100	38	62
	7/13/2013
iPad#	Start	End	Battery Life Used
1	100	60	40
2	100	79	21
3	100	99	1
4	100	98	2
5	100	100	0
6	100	40	60
7	100	2	98
8	100	19	81
9	100	100	0
10	100	100	0

As shown in the Table, the cemetery monument recording work, which generates many more forms and digital images, uses up a lot more battery life.  For the two days in which they recorded cemetery headstones, the student's iPads used between 59% and 86% of battery life.  Because Friday was only a five-hour day, and Thursday was a training day when the new crews were getting oriented to the recording strategy, the average battery use might be a bit more for a fully trained crew over an 8 hour workday.  The average for Thursday of 79.3% is probably conservative.  

Ignoring the partial days and charging glitches, the other seven iPads measurements over the five days is 35 observations of battery use.  The average use was 34.0% of the battery with a standard deviation of 24.26.  There was a significant range between no use (the iPad was not used) and 98% of battery use. As iPads are tied to particular excavation units, no use indicates that those units were not excavated that day.  Excavation tasks included filling out the four-page level form, taking images, and some intensive use of iDraw to map the World War I railroad grade. I think a fully trained professional field crew (excavating at a rate of 2 10-cm levels per person per day) will likely generate more forms and perhaps use more battery life depending on the complexity of the site.   Even so, there appears to be plenty of capacity for excavation forms and digital images. This is consistent with the results from other projects, such as the Pyla-Koutsopetria Archaeological Project on Cyprus and the E'se'get Archaeology Project in Nova Scotia.