== Installation A typical installation involves attaching only a suitable battery, a single pole switch for power on/off, and two pairs of wires connecting e-matches for the apogee and main ejection charges. All Altus Metrum products are designed for use with single-cell batteries with 3.7 volts nominal. EasyMini may also be used with other batteries as long as they supply between 4 and 12 volts. The battery connectors are a standard 2-pin JST connector; you can purchase suitable batteries from the any vendor selling Altus Metrum products. These batteries are single-cell Lithium Polymer batteries that nominally provide 3.7 volts. Other vendors sell similar batteries for RC aircraft using mating connectors, however the polarity for those is generally reversed from the batteries used by Altus Metrum products. In particular, the Tenergy batteries supplied for use in Featherweight flight computers are not compatible with Altus Metrum flight computers or battery chargers. [WARNING] Check polarity and voltage before connecting any battery not purchased from Altus Metrum. [WARNING] Spark Fun sells batteries that have a matching connector with the correct polarity. However, these batteries include an integrated current limiting circuit. That circuit will cause the battery to shut down when firing the igniter circuit. Do not use these batteries unless you remove the current limiting circuit. By default, we use the unregulated output of the battery directly to fire ejection charges. This works marvelously with standard low-current e-matches like the J-Tek from MJG Technologies, and with Quest Q2G2 igniters. However, if you want or need to use a separate pyro battery, check out <<_using_a_separate_pyro_battery>> for instructions on how to wire that up. The altimeters are designed to work with an external pyro battery of no more than 15 volts. Ejection charges are wired directly to the screw terminal block at the aft end of the altimeter. You'll need a very small straight blade screwdriver for these screws, such as you might find in a jeweler's screwdriver set. ifndef::telemini[] The screw terminal block is also used for the power switch leads. endif::telemini[] ifdef::telemini[] Except for TeleMini v1.0, the flight computers also use the screw terminal block for the power switch leads. On TeleMini v1.0, the power switch leads are soldered directly to the board and can be connected directly to a switch. endif::telemini[] ifdef::radio[] For most air-frames, the integrated antennas are more than adequate. However, if you are installing in a carbon-fiber or metal electronics bay which is opaque to RF signals, you may need to use off-board external antennas instead. In this case, you can replace the stock UHF antenna wire with an edge-launched SMA connector, and, on TeleMetrum v1, you can unplug the integrated GPS antenna and select an appropriate off-board GPS antenna with cable terminating in a U.FL connector. endif::radio[]