1978 Johnson 175, 200, 235 HP Outboard Service Manual, Page 142Get this manual
Specific gravity will vary points (.004) with every 10 0F (6 C) temperature changeFor each 10 (6 e) below 80 (27 C), subtract points from hydrometer readingFor each 10 (6 C) above 80 F(27 C), add pOints to hydrometer readingAfter correcting to 80 (27 C), interpret eadings as follows1All cell readings uniform and above 1225 specific gravityBattery is serviceableMay require charging2All cell readings uniform and below 1225 specific gravityRecharge to full charge and retestSee note3Variation of more than 30 points (.030) specific gravity between any two cellsBattery condition is questionableRecharge and retest before making replacementNOTE Disconnect batterypositive cable when charging