I have searched on Google but can't find anything. Could anyone please tell me what a maintenance free battery is? Perhaps some examples of maintenance free batteries and any good sites for further research could be provided.
The term "Maintenance Free Battery" is typically applied to sealed lead-acid batteries such as used for UPS units.
Traditional lead-acid batteries for automobiles needed the battery electrolyte topped up from time to time with distilled water, whereas the maintenance free ones neither need, nor support such maintenance.
mantainance free bateries are the sealed ones, which you can't add clean water+sulphuric acid except in some cases i've seen people perforates the battery to reuse them mostly for a short time-period results as the sealed batteries have thinner lead plates which consume as fast as the chemicals so it would give you a margin of a months? until you replace them for newer ones