From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Performance chart logging average amperes and ampere-hours over time.
| Identifier | ExFiles\Box 58\3\ Scan196 | |
| Date | 7th January 1930 | |
| 5 6 7 8 9 10 11 12 1 2 3 4 7-1-30 224 PPR + Exide N.S.I. 111/LOC 75 ah. 2 Average amperes = 6.34 Hours = 9.7 Ampere hours = 61.5 .554 1.80w REGD TRADE MARK "EVERETT" | ||