此類充電器構造簡單：一般由電源變壓器和四個二極管構成的橋式整流電路組成。充電的整個過程電壓保持不變，當電池的內阻隨著充電過程越來越小，因此充電電流也越來越大，產生的熱量也越來越多。電池快充飽時發熱量最大。加速電解質的分解，從而縮短了電池的壽命。早期的廠家生產的充電器采取“小心駛得萬年船”的(de)(de)策略，用(yong)(yong)小電(dian)(dian)流充電(dian)(dian)，一般(ban)不(bu)超過100mA ，這樣電(dian)(dian)池充到最(zui)后，發熱不(bu)至于太大(da)，從而延(yan)長電(dian)(dian)池壽命。缺點是充電(dian)(dian)時間(jian)長。現在(zai)生產這類(lei)的(de)(de)廠(chang)家，采用(yong)(yong)中電(dian)(dian)流充電(dian)(dian)，100～200mA 充電(dian)(dian)時間(jian)大(da)大(da)縮短，但是以犧牲電(dian)(dian)池壽命為代價(jia)。傻(sha)瓜型充電(dian)(dian)器(qi)只能(neng)用(yong)(yong)時間(jian)來控制(zhi)充電(dian)(dian)，它(ta)只適合于深(shen)充深(shen)放(fang)的(de)(de)五號、七(qi)號鎳鎘、鎳氫電(dian)(dian)池。

    充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)間(jian)：T = 1.5C/I（ C是(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)池容量(liang)，I是(shi)(shi)(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)）例：如果(guo)有個1000mAh 的(de)(de)電(dian)(dian)(dian)(dian)(dian)池放(fang)在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)是(shi)(shi)(shi)50mA的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器上充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)間(jian)就是(shi)(shi)(shi)30小時(shi)。辨認這類充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器的(de)(de)方法：當插上電(dian)(dian)(dian)(dian)(dian)源(yuan)插頭后，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)指示燈(deng)一直(zhi)亮著。街上賣的(de)(de)10～40元以內的(de)(de)均是(shi)(shi)(shi)這種充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器。