Hydrometer, to check batteries

last updated : 2019/03/19
Code Description Budget Price Ship. weight Ship. vol.
BATTERY TESTER, hydrometer check electrolyte density, plast. CH 19.00 0.1kg 1L Add

General information

The hydrometer measures the density of a fluid. In the case of the battery electrolyte, the density will indicate the charge of the battery. It can also be used to check the quality of electrolyte when buying it for new batteries.

Electrolyte: This is a dilution of sulphuric acid in distilled water at a concentration of around 25%.
The specific weight must be 1.23 at 25°C ambient. It is 1.25 at 20°C, and 1.21 at 30°C. Before purchasing, it is recommended to measure the specific weight with an hydrometer. Good hydrometers are graduated, you can read the specific weight, the cheap one’s show a red/white/green scale, the reading must be in the green zone. One should also ensure the containers are sealed and the tamper proof device is not damaged.

  • Exceptionally, electrolyte can be prepared from sulphuric acid at 90% added to distilled water. This is a dangerous process. It must be made in plastic containers with plastic instrument only. The procedure is to add step by step small quantities of acid into a large volume of water. Doing the opposite would create a high temperature chemical reaction spilling acid all around.
  • In some remote areas, rain water can be collected directly as distilled water. It must be directly collected into a plastic container, not from the iron sheet roofs and gutters. It can be kept months in opaque plastic containers, in the dark.
  • Once a battery has been filled with electrolyte (battery acid) never add acid again, add only distilled water.


Hydrometer for battery electrolyte, graduated, plastic.