diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp b/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp
new file mode 100644
index 0000000000..d2caa4968a
--- /dev/null
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp
@@ -0,0 +1,36 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <AP_Common.h>
+#include <AP_HAL.h>
+#include "AP_BattMonitor.h"
+#include "AP_BattMonitor_Backend.h"
+
+/*
+  base class constructor.
+  This incorporates initialisation as well.
+*/
+AP_BattMonitor_Backend::AP_BattMonitor_Backend(AP_BattMonitor &mon, uint8_t instance, AP_BattMonitor::BattMonitor_State &mon_state) :
+        _mon(mon),
+        _state(mon_state)
+{
+}
+
+/// capacity_remaining_pct - returns the % battery capacity remaining (0 ~ 100)
+uint8_t AP_BattMonitor_Backend::capacity_remaining_pct() const
+{
+    return (100.0f * (_mon._pack_capacity[_state.instance] - _state.current_total_mah) / _mon._pack_capacity[_state.instance]);
+}
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_Backend.h b/libraries/AP_BattMonitor/AP_BattMonitor_Backend.h
new file mode 100644
index 0000000000..9c02a299f9
--- /dev/null
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_Backend.h
@@ -0,0 +1,44 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __AP_BATTMONITOR_BACKEND_H__
+#define __AP_BATTMONITOR_BACKEND_H__
+
+#include <AP_Common.h>
+#include <AP_HAL.h>
+#include "AP_BattMonitor.h"
+
+class AP_BattMonitor_Backend
+{
+public:
+    // constructor. This incorporates initialisation as well.
+    AP_BattMonitor_Backend(AP_BattMonitor &mon, uint8_t instance, AP_BattMonitor::BattMonitor_State &mon_state);
+
+    // we declare a virtual destructor so that BattMonitor driver can
+    // override with a custom destructor if need be
+    virtual ~AP_BattMonitor_Backend(void) {}
+
+    // read the latest battery voltage
+    virtual void read() = 0;
+
+    /// capacity_remaining_pct - returns the % battery capacity remaining (0 ~ 100)
+    uint8_t capacity_remaining_pct() const;
+
+protected:
+    AP_BattMonitor                      &_mon;      // reference to front-end
+    AP_BattMonitor::BattMonitor_State   &_state;    // reference to this instances state (held in the front-end)
+};
+#endif // __AP_BATTMONITOR_BACKEND_H__