Comparative performance graphs of P&RTBD7 and Exide 6XL3-4 batteries, plotting Volts against Amperes.
| Identifier | WestWitteringFiles\O\2April1926-June1926\ Scan248 | |
| Date | 23th June 1926 | |
| Left Graph: SUSTAINED PD. TRUE E.M.F. STANDARD 20.H.P. P&RTBD7 VOLTS AMPERES Right Graph: SUSTAINED PD. TRUE E.M.F. STANDARD 20.H.P. EXIDE 6XL3-4 AMPERES g.g. 23-6-26 | ||
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).