{"id":12281,"date":"2019-01-09T11:40:01","date_gmt":"2019-01-09T09:40:01","guid":{"rendered":"https:\/\/www.victronenergy.com\/blog\/?p=12281"},"modified":"2021-06-21T13:20:02","modified_gmt":"2021-06-21T11:20:02","slug":"lead-acid-battery-charging-in-cold-weather","status":"publish","type":"post","link":"https:\/\/www.victronenergy.com\/blog\/2019\/01\/09\/lead-acid-battery-charging-in-cold-weather\/","title":{"rendered":"Lead acid battery charging in cold weather"},"content":{"rendered":"

This blog covers lead acid battery charging at low temperatures. A later blog will deal with lithium batteries.<\/p>\n

Charging lead acid batteries in cold (and indeed hot) weather needs special consideration, primarily due to the fact a higher charge voltage is required at low temperatures and a lower voltage at high temperatures.<\/p>\n

Charging therefore needs to be ‘temperature compensated’ to improve battery care and this is required when the temperature of the battery is expected to be less than 10\u00b0C \/ 50\u00b0F or more than 30\u00b0C \/ 85\u00b0F. The centre point for temperature compensation is 25\u00b0C \/ 77\u00b0F.<\/p>\n

Cold weather also reduces a battery’s capacity. This is another factor that needs to be taken into consideration, along with the load and charge rate compared to the battery capacity (Ah). Both of these factors affect the correct and consequent sizing of a battery for your particular application.<\/p>\n

<\/p>\n

Battery capacity in Ah is usually quoted as a 20 hour capacity rating at 25\u00b0C. The discharge rate or load can be written as 0.05C where for example C is the load factor of the 20 hour rated battery capacity at 25\u00b0C.<\/p>\n

Worked examples: If a 100Ah 20hr rated battery then a 0.05 load would be 100 x 0.05 = 5 Amps or 100\/20 which is also a 5 Amp discharge rate over that 20 hour period. A 10A load on a 100Ah 20 hour rated battery would therefore be a 0.1C discharge rate, a 0.2C discharge rate on a 200Ah would be 40A and so on. C ratings also relate to charge rates as well as discharge rates.<\/p>\n

When buying a battery you may see its Ah quoted at 20 (the standard rate), 10 and 5 hour rates so you can see how load ‘shrinks’ the Ah. Some even quote at 25 hour rates, which often fools people into thinking they are getting a bigger battery than standard.<\/p>\n

To recap – capacity reduces at low temperatures, as it does for higher discharge C rates above the 0.05C 20 hour rate. This reduction in capacity due to higher discharge rates is due to Peukert’s Law<\/a>.<\/p>\n

Graph showing the effect on battery capacity due to temperature and load:<\/strong><\/p>\n

\"\"<\/p>\n

Also with regard to temperature be careful not to let your lead acid battery freeze. The freezing point depends on its state of charge and the specific gravity of the electrolyte. Without getting into the complexities, suffice to say maintain the battery in a fully charged state, as at low states of charge the electrolyte is more water like and freezes earlier than in a fully charged state.<\/p>\n

Lead acid battery differences<\/h3>\n
Lead acid batteries come in a variety of types:<\/div>\n