A magic item can be designed to store Chi points. In general, these store two points of either Magic, Fortune, or Fu. These recharge at the usual rate - once per session for Magic, Fortune, once per sequence for Fu.
By putting restrictions on what these points can be used for, the capacity can be increased. Restricting them to a specific sorcery schtick or Fu path increases capacity to three, and limiting it to a specific sorcery effect or fu/creature schtick increases it to five. A Fu battery that only recharges between sessions instead of between sequences has double the usual capacity.
In no case can you store more points than you have in the relevant attribute, nor can you spend more points on any single task than you have in the relevant attribute.