Compaselect HydroVolt


(1 customer review)

Compaselect HydroVolt battery hydrometer, a great hydrometer for a very modest price

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SKU: COM-181-100 Categories: , Tags: , ,

The Swiss-designed HYDROVOLT battery tester is a heavy-duty, chemical-resistant hydrometer which is direct reading and with build-in temperature compensation accurate at all electrolyte temperatures. Its advanced design incorporates important practical features which simplify battery service as never before; this is the easiest-to-use hydrometer out there. It is also very accurate, beating out any turkey-baster type, and equaling much more expensive refractometers. We at Solacity use a HydroVolt hydrometer ourselves to keep tabs on our forklift battery!

It is a very good idea to take regular hydrometer readings of your flooded lead-acid battery cells. In particular right after a full charge, when it is easy to see if you have a problem with sulphating. Specific gravity readings with a hydrometer are the only accurate way to see what is happening inside your (expensive) deep cycle batteries, and are a way to catch issues when they can still be corrected, before they become a problem.

Regular (say once-every-two-months) hydrometer readings, and keeping a log of those readings for each cell (number the cells with a Sharpy) will also go a long way if it is ever necessary to make a warranty claim with a battery manufacturer. You will stand much stronger when you can show with a log that the battery was maintained well, but despite that a cell just went ‘bad’, it happens.

These are Specific Gravity values for regular deep-cycle flooded lead-acid batteries versus the State-Of-Charge of the battery cell:

% State-Of-Charge (SOC) Specific Gravity (SG)
100% 1.255 – 1.275
75% 1.215 – 1.235
50% 1.180 – 1.200
25% 1.155 – 1.165
0% 1.110 – 1.130

The HydroVolt is identical to MidNite Solar’s ‘MNHydrometer’ product. Solacity just imports them directly from the manufacturer in Europe, we do not get them from MidNite Solar.


  • Handy compact size for use with hard-to-get-at batteries
  • Large, easy-to-read scale with quick-check coloured sectors
  • Readings independent of vertical positioning of instrument
  • Fast, bubble-free intake of fluid sample
  • Automatic air-lock prevents fluid loss and air bleed
  • Unrivalled automatic temperature compensation and measuring accuracy
  • Sturdy, shock-resistant materials, noncorrosive throughout

For the modest price this is truly the best hydrometer out there, and a must-buy for anyone with flooded lead-acid batteries!

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Mnfr. model

1 review for Compaselect HydroVolt

  1. Bob

    This is a great tool, just bought my second one.
    I also have a very nice glass float type with built in thermometer for temperature compensation, but the Hydrovolt is far simpler and more repeatable.
    One squeeze of the bulb fully fills the measuring chamber, a quick tap in case there are any bubbles ( generally not because the hose can stay submerged when filling) and you get a temperature compensated specific gravity.
    With my conventional hydrometer, I have to get rid of the bubbles, make sure the float is “floating” by adding or subtracting acid, make sure I am not squeezing the bulb at all, ad then try to see which ring on the float is at the surface.
    Highly recommended if you are checking specific gravity beyond seeing if it is in the green zone or not.

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