More batteries are damaged by bad charging methods than all other causes combined.
NiMH battery (Nickel-Metal Hydride battery):
The average charging time for the NiMH battery is about 1.5 - 2 hours. When you are charging always pay attention and make sure not to overcharge the battery. Proper charging of NiMH batteries is important to optimize performance in any product. For a fully discharged NiMH battery, an approximate charge time can be calculated using the following formula:
Battery mAh capacity X 120% ÷ mA charge rate = hours of charge.
The battery capacity can be found on the battery label. The charge rate of the charger can be found on the product datasheet.
Li-ion battery (Lithium-ion battery):
There is only one way to charge lithium-based batteries. The so-called 'miracle chargers', which claim to restore and prolong batteries, do not exist for lithium chemistries. Neither does super-fast charging apply. Manufacturers of lithium-ion cells have very strict guidelines in charge procedures and the pack should be charged as per the manufacturers "typical" charge technique.
Lithium-ion is a very clean system and does not need priming as nickel-based batteries do. The 1st charge is no different to the 5th or the 50th charge. Stickers instructing to charge the battery for 8 hours or more for the first time may be a leftover from the nickel battery days.
Most cells are charged to 4.20 volts with a tolerance of +/?0.05V/cell. Charging only to 4.10V reduced the capacity by 10% but provides a longer service life. Newer cell are capable of delivering a good cycle count with a charge to 4.20 volts per cell.
LiPo, Li-Poly battery (Lithium-ion polymer battery):
Lithium Polymer or Lithium Ion cells offer many advantages for the model flier. Their small size and light weight makes them ideal for use in electric models, and they are an ideal companion for brushless motors. Because they are small, they will fit in models that would previously take a low voltage and small amperage NiCad. The lighter weight means lower wing loading on the wings, improving low speed handling, the aerobatic performance and higher top speeds. So a training model will be easier to take off and land, and will fly better and a performance model will be better in all respects, with easier manoeuvres. The model will also have less kinetic energy to dissipate in the event of a mishap, so it is likely to be less severely damaged.
However, these batteries do present some dangers, and care must be taken with them, more care than NiCads. Some investment is required to buy a suitable charger, a wattmeter and balancing unit, and the cost of the battery itself is normally higher, although the costs are coming down as the technology improves.
The dangers are minimal if suitable precautions are taken as outlined in this page, and the benefits are considerable.
Safety Tips - LiPo batteries
Charging
• Be absolutely sure that the Lithium Polymer charger settings are correct for the battery pack being charged – both voltage and current settings
• Care should be taken to charge on a fireproof surface, such as brick.
• Do not charge batteries near flammable items or liquids
• Keep a dry fire extinguisher nearby - or a large bucket of dry sand, which is a cheap and effective extinguisher.
• Do not charge inside an automobile, especially while driving
• Batteries should NEVER be left unattended while charging
The charge voltage of a lithium cell goes down with temperature. At room temperature the charge voltage is 4.2V, at near freezing it is about 4.1V. If you charge at room temperature fully and then take the pack on a winter’s day to the flying field (or store it) and its temperature gets down to 10deg C or less it will may "puff" because it will be overcharged at this temperature! Better to charge to 80% (4.1v/cell) or run the battery down a bit on a cold day or putting in storage.
Handling Caution - LiPo batteries
New cells may have a high initial charge, and care must always be taken to insure that loose cells are not short circuited. Please:
• Do not put the loose cells in a pocket, bag, or drawer where they could short-circuit against other items, or the battery tabs could be pressed against each other.
• Do not place the loose cells on any conductive surface, such as a metal-topped table.
• Keep loose cells and battery packs WELL out of reach of children!
• Buy pre-assembled packs from an authorized dealer, rather than assembling packs from loose cells. You need specialist solders to connect onto the cell ends anyway
• Take care that the cells are not punctured, especially by metallic objects like hobby knives.
• If the electrolyte in the cells should get on your skin, thoroughly wash with soap and water. If in the eyes, rinse thoroughly with cool water. Immediately seek medical attention for this, or for burns.
• Although environmentally friendly, lithium polymer cells must be FULLY discharged before disposal. Use a resistor setup (light bulbs, for example) to accomplish this, to avoid the possibility of a short-induced fire after disposal.
• A punctured pack may be left OUTDOORS in salt water for 2 days to discharge.
General Do's and Don’ts for rechargeable batteries:
Do's
DO follow the manufacturer’s directions carefully for battery storage and care, and don’t overcharge batteries.
DO charge on a surface that cannot catch fire
DO charge your battery at room temperature (68°F to 72°F) to extend battery life. Batteries get warm during charging and use—this is normal. As a precaution, most batteries and chargers are designed to protect against overheating.
DO remember to recharge your battery a few hours before you want to use it. Rechargeable batteries lose a percentage of their charge each day when left off the charger.
DO keep battery contact surfaces clean by gently rubbing with a clean pencil eraser, cloth or rubbing alcohol. Dirty contact points are a primary source of charging challenges.
DO use only chargers designed for your type of batteries. If unsure about compatibility, contact the product manufacturer.
Don'ts
DON’T charge on carpets, paper or any other surfaces that can catch fire
DON’T leave your rechargeable batteries discharged or unused for extended periods of time. To extend battery life, charge them at least every 6-9 months.
DON’T recharge a battery unless it is specifically marked “rechargeable.” Attempting to recharge a primary (non-rechargeable) battery could result in leakage or rupture.
DON’T use rechargeable batteries in chargers that are not designed for the specific battery type.
