«Work done, have fun» would be an ideal scenario when you buy a car battery. But this is not how it’s supposed to be because battery charge level should be checked not only after you get into an emergency situation. It needs to be under control, and every car enthusiast should know how to recharge a car battery, if necessary.

How to recharge a car battery

To charge or not to charge – that is the question

Even a not very experienced driver can determine whether a battery needs to be charged. It is not only about cases when you cannot start your vehicle at all: for instance, poor operation of electrical appliances during engine start can also be an alarming symptom. But you need to confirm your fears, and before reviving the car battery, you need to determine whether it really needs charging. There are several ways:

  • Measure the voltage at the terminals. 12.7 volts — it is desirable for a car enthusiast to know this value: it means 100 percent battery charging. If the tester shows 12.2 volts, the battery is half charged, and when you see 11.6 or 11.7, it means that you should definitely take measures to charge it: your battery is low.
  • Measure the density of the electrolyte. The method is informative, but it is suitable only for maintainable batteries. If the absence of a sealed housing allows you to get to the electrolyte reservoirs, you should know that electrolyte density is measured by a hydrometer. 1.27 g /cm3 is the maximum density, if the value is significantly less, you should charge your car battery with a charger.

How to measure the voltage at the terminals

Your main enemy here is overcharging

Ask some car enthusiasts whether you should charge a battery without removing its terminals, and you will find out that polarity exists not only in batteries but in people’s answers as well. Experts’ points will surely become accompanied by a comment from an experienced car enthusiast like “I remember I had a case”, and the argument will start again.

One may not remove their battery from a car, but as for the terminals — everyone decides for themselves. Charging your car battery with a charger and connecting to the onboard system at the same time may cause the main problem which is overcharging. There are plenty of electronic devices in modern cars now, and each model of electronics has its own parameters concerning the maximum voltage. Therefore, in order to prevent devices from failing, the owner, who decided to leave terminals on the battery, needs to know the lowest value of the maximum tolerable voltage.

Charger vs Generator

There is another relevant question, yet less acute than the previous one: «Which of these devices charges better — a generator or a charger?” The first option may have adherents, but this will mostly be due to the fact that the method of charging from the generator does not require any labour and time – the battery is charged automatically. But if you ask how to charge a car battery properly, without taking into account only the easy availability of the option, the answer will be unambiguous – using a charger. Here are its advantages, which, undoubtedly, are significant:

  • a charger will help to get the best results for batteries which are different in type, degree of discharge and service life;
  • you can use it to control the process parameters;
  • unlike a generator, a charger can charge a battery up to 100% of its capacity.
How to charge the battery with a charger

Is it possible to charge a maintenance free battery at home?

Yes, it is. Just do not disregard the following two points: first of all, you should remember that a key ready battery does not allow you to measure the electrolyte density. Secondly, taking into account the sealed case, rapid charging with large currents is not allowed.

In fact, there is also «thirdly» here, and this point will serve you as a «hint” telling you how to cope with the first two. A lot depends on the charger you use. When charging a maintenance free car battery, it is important to set the current and voltage parameters accurately, so, when choosing a charger, focus on the following points:

  • whether there is an option which allows to limit and adjust voltage;
  • charge current adjustment;
  • control of intermediate cut-offs according to adjustable parameters.

Things are more simple for those who know the basics of battery charging: you can save money and buy a charger without the third option. But it will be necessary to monitor the current values using a multimeter in such a situation on your own. If you don’t want everything to be so complicated, just get a smart charger for maintenance free batteries: you will spend more money but you will also know what you are paying for.

How long should the battery charge

How long will it take?

After we’re done with the questions of whether it is worth charging a battery yourself and how to do it correctly, it is reasonable to clarify how long does it take to charge a car battery. It is quite difficult to give an ultimate answer to this question, since much will depend on the degree of discharge. An information sticker that manufacturers leave on the battery can partly serve as a hint.

Besides, it is important to keep in mind that maintenance free batteries should not be overcharged due to the high probability of intense gas emission. And then there is a chain reaction: electrolyte vapours leave through the safety valve, the liquid level in the reservoirs drops down, which over time can lead to plate exposure and, accordingly, to a decrease in the battery capacity.

In fact, it is not difficult to estimate the right time to charge a battery, one should just solve a problem which can be handled even by those who are much more into humanities. Let’s say the voltage of a 60 ampere hour battery is 12.2 volts — half the charge. Therefore, the charge needs to be set to 30 ampere hours. We divide this figure by the supplied current of 6 amperes (10% of the nominal capacity) and as a result we get no more than five hours of charging.

And so the conclusion is
To properly charge a car battery, you need to:

  • Check the actual charge level;
  • Prepare the device;
  • Stick to the rules of charging stages and its duration;
  • Observe safety precautions.