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).
Comparative table of battery capacity and starting effort for different types.
| Identifier | ExFiles\Box 164\3\ img116 | |
| Date | 21th January 1938 | |
| TYPE 6-HZD9-S 6-LZLD13-S 6-HZD11-S 6-HZD13-S CAPACITY AMPERE HOURS 20 hour rate 54 60 68 81 10 hour rate 49 54 61 73 COMPARATIVE STARTING EFFORT TAKING 6-HZD13-S AS 100. 68 72 83 100 21.1.38 | ||