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Guide to Battery Chargers

This guide is for NiMH rechargeable battery chargers.

There are many different types of battery chargers and they can be categorised in a variety of ways - firstly how they indicate when a battery is charged which can be divided into two types - Manual or ‘Dumb’ chargers and intelligent chargers.

What is a manual charger?

What is an intelligent charger?

What are Fast and Super-Fast chargers?

What type and size of batteries can be recharged?

Do stay-charged or low discharge batteries need a special charger?

How long will it take to charge my batteries?

Do I need to use my rechargeable battery until it is flat before I can recharge it?

Do I need to use the same brand rechargeable battery as my charger?

Can I charge my single-use batteries in my charger?

Is my charger suitable for world-wide use?

Trouble-shooting tips for battery charging

 

What is a manual charger?

A manual battery charger will recharge NiMH batteries continuously and will not shut off when the batteries are fully charged. Typical charge current for AA batteries should be around 120 – 150mA to avoid any over-charging when left on for a period of time.

Usually these chargers have an LED indicator (such as a light) to show the batteries are receiving charge, however these indicators will not change when the battery is fully charged so you will need to calculate the time required by dividing the capacity of the battery with the output of the charger – please see our FAQ on charging times for further details. These chargers deliver a slow, steady charge and can often be advertised as ‘overnight’ chargers.

The main benefit of this type of charger is value for money. They are usually at the lower end of the price range and if you do not need a fast charger they can be a good compromise. The disadvantages are that you won’t know exactly when your batteries are fully charged. This may mean the batteries are under charged, or left on charge longer than necessary leading to an element of guess work with the charging times - particularly if your battery is not fully discharged (flat) when being recharged. These chargers usually require the batteries to be inserted in pairs to complete the circuit and recharge the batteries.

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What is an intelligent charger?

Also known as ‘Smart’ chargers, this type of charger usually has an LCD display which will indicate the level of charge in the battery – for example if it is half charged, fully charged etc. When the battery is fully charged this will be indicated on the LCD display and the charger will stop charging or revert to a trickle charge to keep the battery topped up. This achieved by incorporating a computer chip or microprocessor into the charger which controls the various aspect of charging, and can usually also detect faulty batteries.

The benefits of an intelligent charger are that the correct amount of charge is delivered so there will be no over or under recharging. Because intelligent chargers have automatic shut-off, this allows them to have a higher power output so providing faster charging than a manual charger, depending on the capacity and size of the battery. They will also usually offer individual channel charging, because a microprocessor controls charging to each individual battery. This allows odd numbers of batteries to be charged, for example one or three, whereas most manual chargers will require batteries to be charged in pairs to compete the charging circuit. It also means there is no issue in charging different battery capacities, or different levels of charge, unlike manual chargers which require similar capacity and charge levels to charge effectively.

The disadvantage of an intelligent chargers is that they are slightly more expensive than a manual charger, however it is worth considering the investment in a good charger as comparable to the investment made in rechargeable batteries. Please also note that 9 volt PP3 size rechargeable batteries will not usually be charged intelligently at a fast charge rate, due to the higher voltage of the battery.

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What are Fast and Super-Fast chargers?

Virtually all intelligent chargers are considered to be ‘fast’, with typical charge times of 1 to 4 hours depending on the capacity and size of a battery. At this rate of charge there should be no detrimental effect on your rechargeable batteries.

By comparison a super-fast charger will typically charge a rechargeable NiMH battery in 15 – 30 minutes. This offers huge convenience, especially if you are left with no replacement batteries which is the big advantage with this type of charger. However the extremely high currents delivered can heat up a rechargeable battery, causing it to deteriorate quickly. It is estimated that a NiMH rechargeable battery might only last for 50 – 75 recharge cycles if charged mostly in a super-fast charger, instead of the average 500 recharge cycles normally achieved.

We therefore recommend that this type of super-fast charger should be used only occasionally, mixed with normal charging at regular intervals. Consider using a super-fast charger as a back up to a normal charger, rather than as an alternative to a normal or intelligent charger, this should allow you to get the most out of your rechargeable batteries.

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What type and size of batteries can be recharged?

Most battery chargers will charge AA and AAA sized rechargeable batteries regardless of whether they are Intelligent or Manual chargers. Some will also charge 9 volt batteries – but be aware that the charging times for 9 volt batteries will be much longer in comparison. Universal chargers will charge a range of battery sizes which usually includes AA, AAA, C, D and 9 volt rechargeable batteries, but always check the product details or contact our customer service team to ensure you find the most suitable charger for your batteries. 

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Do stay-charged or low discharge batteries need a special charger?

No – any type of charger suitable for NiMH rechargeable batteries will charge either stay-charged or standard rechargeable batteries.

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How long will it take to charge my batteries?

If you are using a basic manual charger which does not switch off automatically or indicate when the batteries are fully charged, you will need to estimate the charging time to ensure that you fully charge your rechargeable batteries. There is a straight forward formula which can be applied to calculate this, by dividing the capacity of the battery by the power output of your charger. This information should be detailed on our website in the product details, or on the charger packaging. For example, if your charger is rated at an output of 180 mA (Mili Amp) it will take 11.6 hours to fully charge a 2100 mAh rechargeable battery from flat (2100 mAh ÷ 180 mA = 11.6 hours). If you are not sure what the output of your charger is you can contact our customer service team for more advice.

Do I need to use my rechargeable battery until it is flat before I can recharge it?

NiMH rechargeable batteries can be recharged at any point of capacity (you do not need to fully discharge the battery or wait until it is completely flat), but the sooner you recharge the better, as you will get increased cycle life out of the battery.

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Do I need to use the same brand rechargeable battery as my charger?

Any brand of NiMH rechargeable battery can be used in any battery charger suitable for NiMH batteries – as long as the size is compatible. However we do recommend you use reputable, well-known brands as there are some batteries and chargers of questionable quality on the market.

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Can I charge my single-use batteries in my charger?

For the vast majority of chargers the answer to this question is ‘No’ and you should not recharge any single-use battery in a standard NiMH battery charger. However there are some exceptions where chargers are specifically designed to charge alkaline batteries for a limited number of recharge cycles (typically 6 to 10) by delivering a very low charging current. One example would be the Lloytron Fast charger, which can charge both NiMH rechargeable batteries and single-use alkaline batteries. However these chargers are very much the exception, so please be advised that you should not attempt to recharge single-use batteries such as alkaline or lithium in a standard NiMH battery charger, unless the charger clearly states this is possible.

Other types of rechargeable battery such as nickel cadmium (NiCd) and lithium ion (Li-ion) batteries require specialist chargers designed for each type of battery.

  

Is my charger suitable for world-wide use?

In order for this to be possible, your charger will need to be able to run on an input voltage of 100V to 240V AC (alternating current) – you will also need to ensure you have a suitable adapter for the country you will be using the charger in. All the battery chargers we stock are compatible for world-wide use.

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Trouble-shooting tips for battery charging

No Power/LCD/LED – Check your charger doesn’t require the batteries to be charged in pairs to complete the circuit. This is usually the case with manual ‘dumb’ chargers but can also apply to a small number of intelligent chargers. No Power/LCD/LED – Check the power supply to the unit. If it has a separate power lead check is it inserted into the charger correctly.Batteries are not receiving charge – Most rechargeable batteries should feel slightly warm to the touch when receiving a charge.Batteries are not receiving charge/still flat after a charge - Have the batteries been charged for the correct length of time? ( for example a high capacity battery such as 2700 mAh may need 14 hours to fully charge with a low output charger)

Batteries are not receiving charge/still flat after a charge – Check for any clear plastic (from packaging) still present on the charging contacts in the battery charger.Batteries are not receiving charge/still flat after a charge – Your batteries may need reconditioning. See our Guide for Battery Reconditioning for more details. 

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